WebView: Rename to set/isAlgorithmicDarkeningAllowed

Rename set/getAllowAlgorithmicDarkening to
set/isAlgorithmicDarkeningAllowed according to API council's
feedback in http://b/216369031

Javadoc change will be in a separated patch.

Bug: 214741472
Test: m, m api-stubs-docs-non-updatable-update-current-api
CTS-Coverage-Bug: 214742132
Change-Id: I959508a5b8e18e054d62cd092140aeeaf7f92231