Invert the dependency direction between `yash-syntax` and `yash-env`

[magicant]

• Invert dependency from yash_env::function to yash_syntax::syntax (Introduce dependency injection to yash_env::function::Function::body #652)
• Inject yash_syntax::parser::lex::is_name instead of directly depending on it from yash_env::parser (Refactor is_name to use dependency injection pattern #651)
• Remaining refactoring (Invert the dependency direction between yash-syntax and yash-env #654)
  • Move yash_env::parser::Config::into_lexer to yash_syntax
  • Move Source, Location, and Alias from yash_syntax to yash_env
  • Move decl_util from yash_syntax to yash_env
  • Move Input from yash_syntax to yash_env