[Dynamo][15/N] Merge allow_in_graph/inline/skip trace rules check into trace_rule.lookup (#118971)
Finally we have this PR to merge allow_in_graph/inline/skip trace rules into ```trace_rules.lookup_inner```, where we can define and lookup trace rules at both function level and file level. Going forward, this is the central place that we define and consulte Dynamo trace rule for any function.
* ```trace_rules.looup``` is the API can return allow_in_graph, inline or skip.
* ```skipfiles.check``` is the API can return inline or skip, since we have multiple places that only do inline/skip check.
* I'll move ```skipfiles.check``` to ```trace_rules.check``` as one of the follow-ups.
* Both functions consulte ```trace_rules.lookup_inner``` to get the tracing rule.
To avoid a single big PR, I left a few items as the follow-ups:
* Remove ```skipfiles.py``` and merge the code into ```trace_rules.py```.
* We do double check in ```symbolic_convert.check_inlineable```, will refactor and simplify it. We should only do inline/skip check before generating ```SkipFilesVariable``` and ```UserFunctionVariable```.
* Rename ```SkipFilesVariable``` as ```SkipFunctionVariable```, since we only handle functions.
* The inline/skip reasons are not logged for some cases, since the new lookup framework doesn't always return inline/skip reasons. I'll refactor loggings to record the inline/skip reason in next step.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/118971
Approved by: https://github.com/jansel
