Debug/Fix HMR support

[GeoffCoxMSFT]

HMR seems to have some troubles with different pieces being changed

• Need a module.hot replacement at the index root
• Need to figure out constraints about extension being updated and HMR reloading

[hatpick]

@GeoffCoxMSFT

HMR seems to have some troubles with different pieces being changed

• Need a module.hot replacement at the index root
  What do you mean by the following?
• Need to figure out constraints about extension being updated and HMR reloading