Deprecate and drop String.dropFileProtocol() and Path.adaptedIsAbsolute() extensions

[0x6675636b796f75676974687562]

Since we now have full URI support in okio-extras, which can even decode URL-encoded sequences like %D0%A2%D0%B5%D1%81%D1%82, there's no need for simple heuristics like String.dropFileProtocol() and Path.adaptedIsAbsolute().

In addition to mere refactoring (which should be simple), extra steps should be made:

• Collect real-life SARIF output from existing tools, such as pylint (pylint --output-format=sarif --disable=... --enable=... --output xyz.sarif) etc. Apparently, uri and uriBaseId fields may contain both file:// URIs and local paths, absolute or relative.
• Cover the above scenarios with unit tests.
• Add extra unit tests for cases when uri and/or uriBaseId contain unparseable garbage. The library should handle these cases gracefully, in a predictable and well-documented manner.

Current test coverage doesn't seem enough.