Bind correct FBO when drawing a WebView into a layer.

The WebView was unable to draw into either a standard clipped
layer or the "fading edges" unclipped layer. This CL and its
companion test cases ensure that both work with simple and
complex clips.

Bug: 79619253
Bug: 80443556
Bug: 80477645
Test: atest CtsUiRenderingTestCases:.LayerTests
Merged-In: I0e16b724f74415a61cc2a841ccf4a491f293ac94
Change-Id: I4900222975fc841b11828916878fb0ea6d87dcda