Support Google Maven repositories

Finding all underlying packages is likely to be a bit of trial and errors.
There is no nexus index and but metadata files and a custom HTML index https://maven.google.com/web/index.html and at https://maven.google.com/web/m_index.html

The HTML index uses JS at https://maven.google.com/web/js/gmaven-index.js to custom XML index files and POMs. There is first a master index of groupids at https://dl.google.com/android/maven2/master-index.xml
This master index loads groupid indexes, one for each groupid such as at https://dl.google.com/android/maven2/androidx/privacysandbox/sdkruntime/group-index.xml
Each contains the name and versions of all available name/versions.

Note that there are two base URLs:
- https://maven.google.com/ which is the primary
- https://dl.google.com/dl/android/maven2/ which is where the real files live

We also have regular maven metadata such as at https://dl.google.com/android/maven2/com/google/mlkit/acceleration/maven-metadata.xml

See for example:
- https://dl.google.com/dl/android/maven2/androidx/core/core-splashscreen/maven-metadata.xml
- https://dl.google.com/dl/android/maven2/androidx/core/core-splashscreen/1.0.1/core-splashscreen-1.0.1.pom
- https://dl.google.com/dl/android/maven2/androidx/core/core-splashscreen/1.0.1/core-splashscreen-1.0.1.aar
- https://dl.google.com/dl/android/maven2/androidx/core/core-splashscreen/1.0.1/core-splashscreen-1.0.1-sources.jar