Bubble icon improvements

* The tinting logic isn't good for developers, this change removes that
  logic and respsects whatever icon they provide, HOWEVER, if it is not
  adaptive it gets put on an adapative shape, consistent with launcher
* Updates the dot colour to be based on colour sample from the app icon
  bitmap rather than the notification colour, consistent with launcher
* Updates Notification documentation to reflect changes

Test: manual with Bubbles test app (options for all the icon types)
Bug: 138943209
Change-Id: I8abfcef9ac1dcdd9f74643e84ef40a97385b744b