For OSR compiles, always import from the original entry point in addtion
to the OSR entry point. This gives the OSR compiler a chance
to see all of the method and so properly compute address exposure,
instead of relying on the Tier0
analysis.

Once address exposure has been determined, revoke special protection
for the original entry and try and prune away blocks that are no longer
needed.

Fixes dotnet#83783.

May also fix some of the cases where OSR perf is lagging (though
don't expect this to fix them all).