Mixed mode exception handling (#4777)

Mixed mode exception handling (#4777)

* [mixed] Add beginnings of unwinding support for interp->jit transitions by pushing an LMF frame on the stack when exiting interpreted code.

* [runtime] Add a mono_debug_lookup_source_location_by_il () helper function to lookup a source location using an IL offset.

* [mixed] Add support for mixed mode managed stack walks.

* [interp] Generate line number info for interpreted code, using the same MonoDebugMethodJitInfo structure used by the JIT.

* [interp] Pass the clause index to the MINT_ENDFINALLY opcode. Not yet used.

* [interp] Create a MonoJitInfo structure for each interpreted method. Not yet used.

* [interp] Add a mono_interp_set_resume_state () function which can be used to set the frame/ip the interpreter will resume execution from when execution returns to it.

* [mixed] Add support for mixed mode exception handling by extending the normal JIT exception handling code in mini-exceptions.c to handle interpreted frames as well.

* [jit] Add an Unwinder type to reduce the amount of code duplication when unwinding though interpreter frames.

* [interp] Fix the !ENABLE_INTERPRETER build.

* [interp] Disable an assert which is hit even when running without --interpreter.

* Fix a comment.

* [interp] Fix an assertion. Fix/add comments.