feat(edit): insert an unsimplified key using CTRL-SHIFT-V

This marks the following Vim patches as ported:

vim-patch:8.1.2333: with modifyOtherKeys CTRL-^ doesn't work

Problem:    With modifyOtherKeys CTRL-^ doesn't work.
Solution:   Handle the exception.
828ffd5963

vim-patch:8.1.2350: other text for CTRL-V in Insert mode with modifyOtherKeys

Problem:    Other text for CTRL-V in Insert mode with modifyOtherKeys.
Solution:   Convert the Escape sequence back to key as if modifyOtherKeys is
            not set, and use CTRL-SHIFT-V to get the Escape sequence itself.
            (closes vim/vim#5254)
fc4ea2a72d

vim-patch:8.2.2084: CTRL-V U doesn't work to enter a Unicode character

Problem:    CTRL-V U doesn't work to enter a Unicode character when
            modifyOtherKeys is effective. (Ken Takata)
Solution:   Add a flag to get_literal() for the shift key. (closes vim/vim#7413)
0684e36a7e

Omit getcmdkeycmd() change as it depends on Vim patch 8.2.2062, which
may introduce a potential breakage.

test/functional/editor/mode_cmdline_spec.lua

@@ -3,67 +3,74 @@
 local helpers = require('test.functional.helpers')(after_each)
 local clear, insert, funcs, eq, feed =
   helpers.clear, helpers.insert, helpers.funcs, helpers.eq, helpers.feed
+local eval = helpers.eval
 local meths = helpers.meths
 
-describe('cmdline CTRL-R', function()
+describe('cmdline', function()
   before_each(clear)
 
-  it('pasting non-special register inserts <CR> *between* lines', function()
-    insert([[
-    line1abc
-    line2somemoretext
-    ]])
-    -- Yank 2 lines linewise, then paste to cmdline.
-    feed([[<C-\><C-N>gg0yj:<C-R>0]])
-    -- <CR> inserted between lines, NOT after the final line.
-    eq('line1abc\rline2somemoretext', funcs.getcmdline())
+  describe('Ctrl-R', function()
+    it('pasting non-special register inserts <CR> *between* lines', function()
+      insert([[
+      line1abc
+      line2somemoretext
+      ]])
+      -- Yank 2 lines linewise, then paste to cmdline.
+      feed([[<C-\><C-N>gg0yj:<C-R>0]])
+      -- <CR> inserted between lines, NOT after the final line.
+      eq('line1abc\rline2somemoretext', funcs.getcmdline())
 
-    -- Yank 2 lines charwise, then paste to cmdline.
-    feed([[<C-\><C-N>gg05lyvj:<C-R>0]])
-    -- <CR> inserted between lines, NOT after the final line.
-    eq('abc\rline2', funcs.getcmdline())
+      -- Yank 2 lines charwise, then paste to cmdline.
+      feed([[<C-\><C-N>gg05lyvj:<C-R>0]])
+      -- <CR> inserted between lines, NOT after the final line.
+      eq('abc\rline2', funcs.getcmdline())
 
-    -- Yank 1 line linewise, then paste to cmdline.
-    feed([[<C-\><C-N>ggyy:<C-R>0]])
-    -- No <CR> inserted.
-    eq('line1abc', funcs.getcmdline())
+      -- Yank 1 line linewise, then paste to cmdline.
+      feed([[<C-\><C-N>ggyy:<C-R>0]])
+      -- No <CR> inserted.
+      eq('line1abc', funcs.getcmdline())
+    end)
+
+    it('pasting special register inserts <CR>, <NL>', function()
+      feed([[:<C-R>="foo\nbar\rbaz"<CR>]])
+      eq('foo\nbar\rbaz', funcs.getcmdline())
+    end)
   end)
 
-  it('pasting special register inserts <CR>, <NL>', function()
-    feed([[:<C-R>="foo\nbar\rbaz"<CR>]])
-    eq('foo\nbar\rbaz', funcs.getcmdline())
-  end)
-end)
-
-describe('cmdline history', function()
-  before_each(clear)
-
-  it('correctly clears start of the history', function()
-    -- Regression test: check absence of the memory leak when clearing start of
-    -- the history using ex_getln.c/clr_history().
-    eq(1, funcs.histadd(':', 'foo'))
-    eq(1, funcs.histdel(':'))
-    eq('', funcs.histget(':', -1))
-  end)
-
-  it('correctly clears end of the history', function()
-    -- Regression test: check absence of the memory leak when clearing end of
-    -- the history using ex_getln.c/clr_history().
-    meths.set_option('history', 1)
-    eq(1, funcs.histadd(':', 'foo'))
-    eq(1, funcs.histdel(':'))
-    eq('', funcs.histget(':', -1))
-  end)
-
-  it('correctly removes item from history', function()
-    -- Regression test: check that ex_getln.c/del_history_idx() correctly clears
-    -- history index after removing history entry. If it does not then deleting
-    -- history will result in a double free.
-    eq(1, funcs.histadd(':', 'foo'))
-    eq(1, funcs.histadd(':', 'bar'))
-    eq(1, funcs.histadd(':', 'baz'))
-    eq(1, funcs.histdel(':', -2))
-    eq(1, funcs.histdel(':'))
-    eq('', funcs.histget(':', -1))
+  it('Ctrl-Shift-V supports entering unsimplified key notations', function()
+    feed(':"<C-S-V><C-J><C-S-V><C-@><C-S-V><C-[><C-S-V><C-S-M><C-S-V><M-C-I><C-S-V><C-D-J><CR>')
+
+    eq('"<C-J><C-@><C-[><C-S-M><M-C-I><C-D-J>', eval('@:'))
+  end)
+
+  describe('history', function()
+    it('correctly clears start of the history', function()
+      -- Regression test: check absence of the memory leak when clearing start of
+      -- the history using ex_getln.c/clr_history().
+      eq(1, funcs.histadd(':', 'foo'))
+      eq(1, funcs.histdel(':'))
+      eq('', funcs.histget(':', -1))
+    end)
+
+    it('correctly clears end of the history', function()
+      -- Regression test: check absence of the memory leak when clearing end of
+      -- the history using ex_getln.c/clr_history().
+      meths.set_option('history', 1)
+      eq(1, funcs.histadd(':', 'foo'))
+      eq(1, funcs.histdel(':'))
+      eq('', funcs.histget(':', -1))
+    end)
+
+    it('correctly removes item from history', function()
+      -- Regression test: check that ex_getln.c/del_history_idx() correctly clears
+      -- history index after removing history entry. If it does not then deleting
+      -- history will result in a double free.
+      eq(1, funcs.histadd(':', 'foo'))
+      eq(1, funcs.histadd(':', 'bar'))
+      eq(1, funcs.histadd(':', 'baz'))
+      eq(1, funcs.histdel(':', -2))
+      eq(1, funcs.histdel(':'))
+      eq('', funcs.histget(':', -1))
+    end)
   end)
 end)