fix(codegen): print `#` before private identifier in TS signature key (#25938)

`TSPropertySignature` and `TSMethodSignature` were printing a `PrivateIdentifier` key as `key.name`, dropping the `#`, so `interface I { #x: number }` was printed as `interface I { x: number }`.

This PR switches `oxc_codegen` to delegating to the `PrivateIdentifier` printer, as every other property key site already does. It also applies the same thing to JS printer `oxc-codegen`.

This is not legal syntax anyway - TS rejects it with TS18016, and Oxc parser with "Private identifier '#x' is not allowed in property names" - so this is only reachable from a recovered parse or a hand-built AST. But, since we have this code, it might as well do what you'd expect it to.