os/input.c: parse keycodes in non-string context #7411

cb02137dfa had two mistakes, of the same nature: trans_special() must
be invoked with in_string=false unless the parsing context is a VimL
string. replace_termcodes() and input_enqueue() are low-level
mechanisms where VimL strings do not exist.

keymap.c: adjust double-quote case to satisfy keymap_spec.lua

closes #7410

test/functional/ex_cmds/map_spec.lua

@@ -5,6 +5,7 @@ local feed = helpers.feed
 local meths = helpers.meths
 local clear = helpers.clear
 local command = helpers.command
+local expect = helpers.expect
 
 describe(':*map', function()
   before_each(clear)
@@ -18,4 +19,10 @@ describe(':*map', function()
     feed('\24\25<C-x><C-y>')
     eq(4, meths.get_var('counter'))
   end)
+
+  it(':imap <M-">', function()
+    command('imap <M-"> foo')
+    feed('i-<M-">-')
+    expect('-foo-')
+  end)
 end)