Add/Fix lingering Task property annotations

[AndrewTasso]

What does this PR do?

• Add/Fix lingering Task property annotations that are causing build issues
  • CacheableReportTask.groovy
    • Apply the @ClassPath normalization strategy to the classpath task property
  • CheckLicenseTask.groovy
    • Declare config as a @Nested task property
    • Apply the ABSOLUTE path sensitivity to allowedLicenseFile task property
    • Apply the ABSOLUTE path sensitivity to projectDependenciesData task property
  • LicenseReportExtension.groovy
    • Apply annotations to properties that tasks use transitively
      • Declare renderers as a @Nested task property
      • Remove renderers explicit public visibility modifier to make the validator happy
      • Declare renderer as a @Nested task property
      • Increase the visibility of the licenseReportExtensionSnapshot task property to public (from private) to leverage the existing @Input annotation

Why was this PR opened?

The build is currently failing due to the validatePlugins task failing. Some changes were made in #159 to resolve Gradle 6.0 deprecations, which resulted in the resolution of #162, but it looks like there were a handful of lingering issues with task annotations after the integration of those changes. This PR fixes the remaining issues that are causing the build to fail

Are there changes in the PR that require closer review?

• LicenseReportExtension.groovy
  • Should the visibility of licenseReportExtensionSnapshot been increased, or annotation removed? I couldn't find any usage of it.
• CheckLicenseTask.groovy
  • Is ABSOLUTE path sensitivity ok for the allowedLicenseFile and projectDependenciesData task properties?

Does this PR meet the usual acceptance criteria?

• [x] Project Builds
• [x] Tests pass
• [x] Document generates successfully with no errors or warnings

Related Issues / PRs

• #159
• #162

[guenhter]

Could you resolve the conflicts?