Pre-built images that reference a parent but specify a tag that is not in the main variant list get the incorrect version

[Chuxel]

Currently the build system tries to match the correct versioned image tag when building an image that depends on another image generated by the repository. For example, jekyll references mcr.microsoft.com/vscode/devcontainers/ruby:2 and has a dependency set to ensure the ruby image is built first.

This logic is not properly handling the "variantTags" property. For example, in ruby's build config:

		"tags": [
			"ruby:${VERSION}-${VARIANT}"
		],
		"variantTags": {
			"3.0": [ "ruby:${VERSION}-3" ],
			"2.7": [ "ruby:${VERSION}-2" ]
		}

In this case the version "2" is not detected since its an additional tag assigned to another image build (for 2.7 in this case). The end ressult is it gets the "latest" tag of 3.0 which is incorrect.

[Chuxel]

Added a specific parentVariant property to definition-manifest.json that is used to make the right determination rather than relying on automated logic or regex scanning. It then errors if something like 3 or 2 is specified in the example above to ensure nothing unexpected slips through.