Add RemoveRedundantDependencyVersions.Skip marker

[Jenson3210]

Summary

• Add a Skip marker nested class in RemoveRedundantDependencyVersions that prevents version removal when present on a dependency tag
• Check for the marker in both isDependencyTag() and isManagedDependencyTag() branches of visitTag
• Revert the previous retainExplicitVersion flag approach in favor of this marker-based design

Problem

When UpgradeDependencyVersion upgrades a dependency to match the parent-managed version, RemoveRedundantDependencyVersions subsequently removes the explicit <version> tag. In some cases, users want to retain the explicit version even when it matches the managed version, but there was no way for an earlier recipe to signal this intent.

Solution

Instead of adding a configuration flag to UpgradeDependencyVersion, introduce a RemoveRedundantDependencyVersions.Skip marker that any recipe can place on a <dependency> tag. When RemoveRedundantDependencyVersions encounters this marker, it skips version removal for that tag. This keeps the mechanism generic and avoids adding recipe-specific boolean flags.

Test plan

• Existing RemoveRedundantDependencyVersionsTest tests pass (56 tests)
• New SkipMarker nested test class with two tests:
  • dependencyWithSkipMarkerKeepsVersion - version preserved when marker present
  • dependencyWithoutSkipMarkerHasVersionRemoved - default behavior unchanged
• UpgradeDependencyVersionTest tests pass

Fixes moderneinc/customer-requests#1942

[steve-aom-elliott]

Is there not the possibility that their explicit versions will be wiped out anyway at some point if something like this is reached (possibly even for a different invocation of UpgradeDependencyVersion that is unrelated)?