Remove IndexingConfig and merge its constants into PropertyConfig.

With 4-tab indents, these nested structures become difficult to write
and maintain. The information encoded here doesn't seem to benefit from
being separated into its own config.

Test: atest CtsAppSearchTestCases FrameworksCoreTests:android.app.appsearch FrameworksServicesTests:com.android.server.appsearch.impl
Bug: 145635424
Change-Id: I6c771e0af1ca34a05b09d1532f0f227a069e0d2e