Comment detecting problem in the command source

[ouuan]

As stated in https://vimhelp.org/cmdline.txt.html#:comment:

It is not possible to add a comment to a shell command ":!cmd" or to the ":map" command and a few others (mainly commands that expect expressions), that see the '"' as part of their argument:"

But in handleExSourceCommand, this is not considered:

FakeVim/fakevim/fakevimhandler.cpp

Lines 6591 to 6594 in 3333aa1

	// remove comment
	int i = nextline.lastIndexOf('"');
	if (i != -1)
	nextline = nextline.remove(i, nextline.size() - i);

This was originally discovered in cpeditor/cpeditor#828, where nnoremap <Space>c :norm ggVG"+ is sourced and becomes ggVG without "+.

A quick fix is to detect whether the " is at the start of a WORD, and maybe also add a special check for map. But it will be better if FakeVim can strictly follow how Vim does this.