[TCWG-614] Long branch thunks: Implemented a prototype of the existing Thunk implementation using Synthetic (Linker created sections) and moved it close to the area it will need to go for Long Branch Thunk work. Worked on this exclusively all week.

Plans for next week: [TCWG-614] Long branch thunks: Tidy up and refactor prototype to a point where I can post for upstream review. This won't be long-branch thunk support but it will be a significant intermediate step.

Do a draft plan of Connect submission and decide how long I need.