refactor($parse): add lgalfaso's refactors and suggestions

[rodyhaddad]

@lgalfaso's PR #7543 had two aspects of it that I didn't include in my last changes to $parse (#7552, #7555)

• Lexer should only take care of constant, and the Parser should deduce that a primary constant is also a literal
• Simplify the logic of Parser.filter

[mary-poppins]

Thanks for the PR! Please check the items below to help us merge this faster. See the contributing docs for more information.

• Uses the issue template (#7571)

If you need to make changes to your pull request, you can update the commit with git commit --amend.
Then, update the pull request with git push -f.

Thanks again for your help!

[lord2800]

The $log annotation is still present here, but the variable was removed?

[rodyhaddad]

Oops!
Fixed, thank you :-)