fix(snippet): cancel session on ESC in insert-mode #41555

Problem:
If a snippet does not have a placeholder, we use insert mode instead of
select mode. From here <Esc> leaves the session and highlight active.

Solution:
Cancel the session on <Esc>.

runtime/lua/vim/snippet.lua

@@ -480,7 +480,7 @@ local function setup_autocmds(bufnr)
     desc = 'Stop the snippet session when leaving select mode',
     buf = bufnr,
   }, function(args)
-    if args.match ~= 's:n' then
+    if args.match ~= 's:n' and args.match ~= 'i:n' then
       return
     end
     vim.schedule(function()

test/functional/lua/snippet_spec.lua

@@ -280,6 +280,16 @@ describe('vim.snippet', function()
     poke_eventloop()
     eq(false, exec_lua('return vim.snippet.active()'))
     eq(0, #api.nvim_buf_get_extmarks(0, ns, 0, -1, {}))
+
+    feed('dal')
+    test_expand_success({ 'local $1 = ${2:value}' }, { 'local  = value' })
+    eq('i', fn.mode())
+    eq(true, exec_lua('return vim.snippet.active()'))
+    t.neq(0, #api.nvim_buf_get_extmarks(0, ns, 0, -1, {}))
+    feed('<Esc>')
+    poke_eventloop()
+    eq(false, exec_lua('return vim.snippet.active()'))
+    eq(0, #api.nvim_buf_get_extmarks(0, ns, 0, -1, {}))
   end)
 
   it('stop session when jumping to $0', function()