graphics: add Composer to HAL support library

Extract IComposer implementation from HwcHal and move it to the HAL
support library.  This requires removal of

  ComposerHal::removeClient
  ComposerHal::enableCallback

and addition of

  ComposerHal::dumpDebugInfo
  ComposerHal::registerEventCallback
  ComposerHal::unregisterEventCallback

since HwcHal does not own a client to send the events to anymore.

Test: boots and VTS
Change-Id: I491e3d2c31d686661d4d3a44842bcac62cc2b2dc