Simplify exposing external interfaces to Launcher

- Currently, the collection of binders to send to Launcher is inverted
  and managed by OverviewProxyService which has to know about each
  component directly (and a SysUI interface has to be created to support
  this even if there are no other calls in SysUI to that component).

  Instead, we should have each component register itself with the
  ShellController for controllers which can be exposed to an external
  process, and each product can customize which set of controllers it
  needs to support.
- Add missing dump registration for ShellController
- Updating docs for creating remote callable controllers

Bug: 238217847
Test: atest WMShellUnitTests
Change-Id: Icd0ed33bdbd68b1dd9d782b9ba1f5b4a604479ba
Merged-In: Icd0ed33bdbd68b1dd9d782b9ba1f5b4a604479ba