The service implementatoin of selection toolbar

We clone most the render logic from LocalFloatingToolbarPopup to the
DefaultSelectionToolbarRenderService to render the menu items in the
system process. When the rendering is done, the system will notify
the application process events to let the application to position
the rendered content.

The changes also removes unused file SelctionContext. We punt the TC
part to the next release, the file is unnecessary now.

This change is only for the service implementation, the client side
implementation will be done on the next change.

Bug: 190030331
Bug: 205823018
Test: manual.

Merged-In: I3915e8165b4d371700cb5fb9e7eb23d46f39bd5c
Change-Id: I2e704432b1e149ce8dd6853fcad6850cf02b60bb