Implement ProguardSpecInfo in Starlark

This addresses the problem of needing --experimental_google_legacy_api for ProguardSpecProvider used by java_lite_proto_library.

Although the latest Bazel 7 minor release exposes the provider without the need for a flag, the provider is impossible to obtain in prior versions without setting the flag.

Replace the provider with a Starlark version, irregardless of Bazel version. This never fails and if there's a Bazel user that needs it, they are probably already advanced enough to set it up together with everything else.

The risk of always using a starlark version is that some combinations don’t work - like native Android rules with Starlark proto rules. Or Starlark proto rules with native Android rules.

PiperOrigin-RevId: 683101513
Change-Id: I7523438e74a2bd1913e8e05fad2f3af18db7eebd