Inliner: enable inlining of methods with conditional throws (dotnet/coreclr#8038)

Inliner: enable inlining of methods with conditional throws (dotnet/coreclr#8038)

* Inliner: enable inlining of methods with conditional throws

Remove inlining limitation for methods that return values and have
conditional throws. This limitation was most likely a vestige of an
older inlining implementation that did not break trees at inline
call sites.

Also removed the now-unused observation and the `seenConditionalJump`
member variable. Merged ifdef blocks in `impInit`.

Ran full desktop testing, no issues.

Enables a handful of inlines in the various code size suites. For the
most part these slightly increase code size but can often shorten the
non-EH paths in the code.

Commit migrated from https://github.com/dotnet/coreclr/commit/e76da565c106016d604b95f3bb7eadd24ceaf18a