Update the Gazelle Java plugin to handle java_maven_install_file directives in nested directories

[jeffmace]

Create a maven.Resolver for each instance of java_maven_install_file and use that resolver for all files under that directory. There aren't any changes to the default behavior; but nested java_maven_install_file declarations will now work as expected.

Background
The Gazelle plugin parses java_maven_install_file directives in nested directories but doesn't use the file when resolving dependencies. This is a problem for projects that use different Maven repositories for different parts of the repository. The top-level maven_install.json file may have incomplete or extra dependencies than the one configured for the lower level directory.

Testing
The unit tests have been updated to reflect the new interface. Integration tests have been added to confirm the updated behavior for an invalid maven_install.json file.

[jeffmace]

@shs96c - Does this look like a reasonable bug fix to bring in?