give placeholder name to document symbols for decls with empty names

[xdBronch]

closes ziglang/vscode-zig#447
not sure i love <unnamed> but 🤷
are there any other languages that allow such arbitrary identifiers we might be able to take inspiration from?

[Techatrix]

There is no need for a placeholder like <unnamed>. If the symbol name is not valid then render the name token as is:

Suggested change

	\\Method <unnamed>
	\\Method <unnamed>
	\\Constant <unnamed>
	\\Constant <unnamed>
	\\Method ""
	\\Method " "
	\\Constant @""
	\\Constant @" "

[xdBronch]

would it be ok to just always include the @/""? it'd make this logic a lot simpler

[Techatrix]

Symbol names shouldn't need to include the @ or "" unless it's needed for some reason. What I suggest isn't as simple as it could be but at least it should hopefully avoid any further issues we may have with how we display document symbol names:

Identifier names should be displayed without @"" unless they need to be escaped. We can assume that the identifier has already been canonicalized with zig fmt so rendering the raw identifier token is fine.

Test names with string literals can be displayed without "" unless one of these cases applies:

• the string literal is empty
• the string literal has leading or trailing whitespace
• the string literal contains escape sequences
  Otherwise it's possible to have two test names that can't be distinguished from each other.