parser: fix enum field name same as keyword (fix #22455)

[yuyi98]

This PR fix enum field name same as keyword (fix #22455).

• Fix enum field name same as keyword.
• Add test.

enum TypeKind {
	none
	const
	enum
	struct
	interface
	sum_type
	i32
	f64
}

fn type_kind(kind TypeKind) string {
	return '${kind}'
}

fn main() {
	mut ret := type_kind(TypeKind.none)
	println(ret)
	assert ret == 'none'

	ret = type_kind(TypeKind.struct)
	println(ret)
	assert ret == 'struct'
}

PS D:\Test\v\tt1> v run .
none
struct

[spytheman]

Afaik prefixing with @, i.e. @none, @const etc is intended for that purpose.

[yuyi98]

This is not necessary for enum field name.
Because of a spate of antipathy .struct_ / .interface_ / .enum_ / .none_ , inconsistent with other style, I think its processing style, instead of .struct / .interface / .enum / .none .

[spytheman]

I do not know then.
@medvednikov what do you think?

[medvednikov]

I like it. Great job!

[JalonSolov]

I think this is asking for problems, rather than helping anything. For the same reason V doesn't allow both .. and ... in ranges, is it too easy to visually confuse struct with .struct, etc. Especially in certain fonts.