This commit changes the default builder image from
`cloudfoundry/cnb:bionic-platform-api-0.2` to
`gcr.io/paketo-buildpacks/builder:base-platform-api-0.3`. It also
uses a `paketo-buildpacks/builder` image instead of a
`cloudfoundry/cnb` image to test compatibility with lifecycle v2
and uses paketo naming instead of cloudfoundry when mocking builder
interactions.

Some adjustments to lifecycle phases were also made to align more
closely with the pack CLI.

Fixes gh-21066