Android WebView: Deprecate unsafe file urls APIs

Deprecate unsafe:
- WebSettings#setAllowUniversalAccessFromFileURLs
- WebSettings#setAllowFileAccessFromFileURLs
- CookieManager#setAcceptFileSchemeCookies

And direct the users to use WebViewAssetLoader instead.

Bug: 148841999
Test: m offline-sdk-docs -j20
Change-Id: I607d1343cb2aa5baead49ceff6dbac4a4474009c