Prefactor lint for upcoming fmt changes (#16964)

Prefactoring `lint.py` in a few ways:
- Moving the bulk of the logic into a `rule_helper` which will comprise of most of `lint` and `fmt`
- Removing the ambiguity check. This won't hold ground in the "generic implementation" as we already have one ambiguity (`black` for files and targets).
- A few other nits and tweaks

[ci skip-rust]
[ci skip-build-wheels]

src/python/pants/core/goals/fmt.py

@@ -239,8 +239,7 @@ def _get_request_types(
     formatters_to_run = determine_specified_tool_names(
         "fmt",
         fmt_subsystem.only,
-        fmt_target_request_types,
-        extra_valid_names=(fbfrt.name for fbfrt in fmt_build_files_request_types),
+        [*fmt_target_request_types, *fmt_build_files_request_types],
     )
 
     filtered_fmt_target_request_types = tuple(