Proper support for gradle caching
Proper support for gradle caching

Symlinks ~/.gradle to a layer, similarly to how maven is setup now. This enables caching of wrapper distro downloads and build caching (takes advantage of gradle's built in incremental building capabilities, but tasks still need to be opted into it in build.gradle).

PiperOrigin-RevId: 314810957
Change-Id: I89feb9f9c0ae3f0307aff1e8248d0039d5c3cd06

GoogleCloudPlatform/buildpacks,GoogleCloudPlatform/buildpacks,GoogleCloudPlatform/buildpacks,GoogleCloudPlatform/buildpacks