Should raise ParsingError instead of NoMethodError

[ksss]

I found a record type pattern that resulted in a NoMethodError instead of a ParsingError, so I fixed it.

RBS::Parser.parse_type("{1?: 1}")
#=> /Users/ksss/.rbenv/versions/3.3.0-rc1/lib/ruby/gems/3.3.0+0/gems/rbs-3.3.2/lib/rbs/parser_aux.rb:7:in `_parse_type': undefined method `literal' for an instance of RBS::Types::Optional (NoMethodError)

      _parse_type(buf, range.begin || 0, range.end || buf.last_position, variables, require_eof)
      ^^^^^^^^^^^

It seems that if the record key starts with Symbol, String, Integer, true, or false, and is not a literal type, the literal method cannot be called, resulting in a NoMethodError.

Although it is not impossible to optimize the code for each token in detail, I think that using parse_simple is a reasonable fix.

[soutaro]

Thanks! 🙏