Declaring literal syntax kind as keyword breaks precedence parsing

When indexing the parser tables with the next token (ignoring extended identifier behavior for this issue), we do one of two things:

• If the next token is an naked atom s (i.e. a symbol or keyword), we use s as the index
• If the next token is a node (i.e. a literal) of kind k, we use k as the index

These two categories are reasonably disjoint in Lean code, but that is unfortunately not true for embedded languages!

import Lean

declare_syntax_cat cat
syntax char : cat
syntax "char" : cat

elab "test" c:cat : command =>
  IO.println c

-- (choice (catChar "char") (cat_ "char"))
test char

Here the keyword char and the literal kind charKind = `char overlap

Start by reproducing the embedded-language example in the issue and inspect how parser tables index an atom versus a literal node. The issue provides no file or test entry point; done means the char keyword and literal kind no longer overlap in a way that breaks precedence parsing.