Jit: decrement finally nesting level when removing empty trys

Jit: decrement finally nesting level when removing empty trys

For non-funclet EH models, the GT_END_LFIN statement tracks the
nesting level of the associated finally. When removing a try-finally
with an empty try we need to decrement this level for any try-finallys
nested within the associated finally.

Added a test case with several levels of empty try and nesting.

Closes dotnet/coreclr#10621.

Commit migrated from https://github.com/dotnet/coreclr/commit/b65b40426527f7ee1813ea640ecf1701df66007c