WebView: consolidate TEST_MAPPING into single config

No change to logic, only test mapping changes. This moves all WebView
folders to use a single consolidated TEST_MAPPING config, across both
our production code and our test code. The goal is to make sure that
when we change any WebView-related code, we need to run the full suite
of WebView tests to make sure our code is still bug-free.

Bug: 419303926
Test: repo upload (check the automated test runs)
Flag: TEST_ONLY
Change-Id: I37c83c1517211ad1587574deefe18c0c895173ab