Fix groovy gradle classpath conflict

[jamesfredley]

1. Switch groovy to scope 'compileOnly' for the grails gradle plugin
2. Split gradle tasks into a new project grails-gradle-tasks due to process islation in gradle & not having a shared classpath

Without these changes, including grails projects with commands in the gradle classpath will cause a conflict:
conflict on capability 'org.codehaus.groovy:groovy:3.0.24' also provided by org.apache.groovy:groovy:4.0.26 #14756

The following conflict is now occurring on grails-shell and grails-forge generated 7.0.0-SNAPSHOT applications

A problem occurred configuring root project 'Test22'.
> Could not resolve all artifacts for configuration 'classpath'.
   > Could not resolve org.apache.groovy:groovy:4.0.26.
     Required by:
         root project : > org.apache.grails:grails-bom:7.0.0-SNAPSHOT:20250517.183431-81 > org.apache.groovy:groovy-bom:4.0.26
         root project : > org.apache.grails:grails-bom:7.0.0-SNAPSHOT:20250517.183431-81 > org.apache.grails:grails-spring:7.0.0-SNAPSHOT:20250517.183431-81 > org.apache.groovy:groovy-xml:4.0.26
      > Module 'org.apache.groovy:groovy' has been rejected:
           Cannot select module with conflict on capability 'org.codehaus.groovy:groovy:4.0.26' also provided by [org.codehaus.groovy:groovy:3.0.24(runtime)]
   > Could not resolve org.codehaus.groovy:groovy.
     Required by:
         root project : > org.apache.grails:grails-gradle-plugins:7.0.0-SNAPSHOT:20250517.180618-108
      > Module 'org.codehaus.groovy:groovy' has been rejected:
           Cannot select module with conflict on capability 'org.codehaus.groovy:groovy:3.0.24' also provided by [org.apache.groovy:groovy:4.0.26(groovyRuntimeElements)]
> There are 2 more failures with identical causes.

[Copilot]

Pull Request Overview

This PR addresses a dependency conflict by switching the dependency scope for Groovy from implementation to compileOnly, ensuring compatibility with Groovy 3 while preventing inadvertent inclusion of Groovy 4.

• Change dependency declaration for 'org.codehaus.groovy:groovy' from implementation to compileOnly
• Alleviate conflicting version issues between Groovy 3 and Groovy 4 in generated applications