Add `HereDocumentBareTag` token type

Ref: https://github.com/goccy/p5-Compiler-Lexer/issues/36

In the past, bare word that is used as here document tag is
treat as `HereDocumentRawTag`.
Here document that is declared by bare tag expands the variable,
however heredoc which is declared by raw tag doesn't.

So added a new type for here document bare word tag.
Merge pull request #46 from moznion/add_HereDocumentBareTag_token_type

Add `HereDocumentBareTag` token type