Replace Gradle single quote strings with the double quote form
whenever possible. The change helps to being consistency to the
dependencies section where mostly single quotes were used, but
occasionally double quotes were required due to `${}` references.
Rename the `spring-boot-cloudnativebuildpack` module to
`spring-boot-buildpack-platform` and update the the package
name to `org.springframework.boot.buildpack.platform`.
Closes gh-19851