The antlr4-maven-plugin using inconsistent dependencies / requirements

The antlr4-maven-plugin is requiring Maven 3.0 via prerequisites and has a dependency to maven-core (test scoped) which is using version 3.3.9 furthermore there is a dependency to the maven-plugin-api with version 3.0.5 and has a dependency to maven-project version 2.2.1.

Steps to clean this up:

1. The first step is to remove the maven-project dependency and change the scope of maven-core from `test` to `compile` to have acccess to `MavenProject` within the Mojo. (#3096)
2. Upgrade the maven-plugin-api to the same version as maven-core
3. Lifting the minimum required Maven version to 3.3.9 as well. Or maybe to a different level but consistent (prerequisites vs. dependencies). (#3102)

Review the antlr4-maven-plugin Maven configuration and its declared prerequisites and dependencies. Check how maven-project, maven-core, and maven-plugin-api are used by the Mojo, then verify that the dependency versions, scopes, and minimum Maven requirement are consistent with the requested cleanup.

Written by the indexing model from the issue text.