Add StringLiteral#titleize macro method

[makenowjust]

This also adds SymbolLiteral#titleize and MacroId#titleize.

Other case conversion methods (upcase, camelcase, etc) are avialble in macro. So, titleize should not be exception.

One use-case is generating error message from type name.

[straight-shoota]

There are no specs for MacroId and SymbolLiteral and it seems the implementation is missing for those, too.

[makenowjust]

@straight-shoota SymbolLiteral and MacroId implementations delegate to StringLiteral implementation (see here and here). So, no problem.

And, other methods of SymbolLiteral and MacroId lacks their specs too.

[watzon]

Do we have this method on standard strings? If so I must've missed the PR, but if not it would be nice to have it there too.

[straight-shoota]

@watzon This PR uses the exact method as implementation:

crystal/src/compiler/crystal/macros/methods.cr

Line 756 in 2d6dba3

interpret_argless_method(method, args) { StringLiteral.new(@value.titleize) }

It was added in #9204

[watzon]

Yeah I saw that when I was going through the code, I guess I missed the PR. Awesome though, I've wished it was there a number of times.