fix: scope webjars as testAndDevelopmentOnly

[jamesfredley]

Apply changes from apache/grails-forge#600

[matrei]

I'm not sure we need to add grails-bom as a platform to testAndDevelopmentOnly as it is a Spring configuration and we are adding the bom to the Spring Dependency Management Plugin in GrailsGradlePlugin. It seems to work without it.

[jamesfredley]

I was glad to remove grails-bom as a platform on testAndDevelopmentOnly. It appeared to be required when we switched from implementation to developmentOnly (https://github.com/apache/grails-core/actions/workflows/gradle.yml?query=branch%3Awebjars-developmentOnly)

[jamesfredley]

* What went wrong: Execution failed for task ':grails-test-examples-namespaces:bootJar'. > Could not resolve all files for configuration ':grails-test-examples-namespaces:testAndDevelopmentOnly'. > Could not find org.webjars.npm:jquery:. Required by: project :grails-test-examples-namespaces 

[matrei]

* What went wrong: Execution failed for task ':grails-test-examples-namespaces:bootJar'. > Could not resolve all files for configuration ':grails-test-examples-namespaces:testAndDevelopmentOnly'. > Could not find org.webjars.npm:jquery:. Required by: project :grails-test-examples-namespaces 

That's interesting. Gradle seems to be able to resolve the webjar versions in apps generated by Forge, without the platform added.

[matrei]

Aha, this is why the platform is needed in the functional test apps:

grails-core/gradle/grails-extension-gradle-config.gradle

Line 33 in ead0035

springDependencyManagement = false

[jamesfredley]

Based on

grails-core/gradle/grails-extension-gradle-config.gradle

Lines 28 to 34 in ead0035

	grails {
	// WARNING: enabling spring dependency management in core can have unintended side effects.
	// since it loads the bom via a pom file, it can't use a gradle project() reference
	// this means you MUST publish locally via ./gradlew :grails-bom:publishMavenPublicationToLocalBomRepository
	// this causes unexpected version mismatches in the various plugin projects
	springDependencyManagement = false
	}

Given we use project() in these test projects, it appears we need to keep the dependency management plugin disabled and add grails-bom as a platform for testAndDevelopmentOnly.

This is different than generated apps, but we are moving in this direction: #14142