[7.0] Final DSL (implementation) changes

[Jonathing]

This PR marks the current final implementation changes for ForgeGradle's DSL.

This still a work-in-progress but is mostly almost done.

• Removes top-level "WithAccessTransformers" sub-types.
  • This gives all consumers access to the #getAccessTransformer() and related methods, but will throw an error if the at-gradle plugin is not loaded instead. This also aids in Kotlin buildscript compatibility.
• Solidifies current DSL and expectation that DSL changes must only be additive until ForgeGradle 8.0.
• Cleans up even more of the Minecraft dependency resolution by using component metadata rules.
  • This enforces that other dependencies which depends on Forge itself do not attempt to resolve a Forge dependencies that doesn't exist (or was not generated by the mavenizer).
• Better default comparator for the net.minecraftforge.mappings.version attribute provided by GradleUtils Shared 3.3.42.