- No longer assigning ivar/cvars to env. Only locals should be in env.
Removed yylex's last_state. Use lex_state directly and stop modifying it everywhere.
+ Added RubyLexer#process_token_keyword.
Split process_token out to only deal with lvars. gvar/cvar/ivar all handled directly.
Merged a lot of state checks into cleaner case stmts. Fewer returns.

[git-p4: depot-paths = "//src/ruby_parser/dev/": change = 8881]