Move copy of Crossgen2 tasks/targets to runtime repo and build composite image for runtime repo in parallel path (#52579)

* Move all crossgen2 tasks/targets used in Runtime repo to be local to the repo

* Move ResolveReadyToRunCompilers task into the Crossgen2Tasks dll

* Create composite bundle and package
- Note that it doesn't build properly, but hopefully that's a crossgen2 task bug

* Composite image production

* Refactor how composite image creation works
- Move it to allow mixed composite and non-composite r2r in the same build, controlled by the PublishReadyToRunCompositeExclusions list
- Enhance the accuracy of how msbuild tracks which files are input vs reference for composite images
- Implement the R2R exclusion list for composite images
- Remove the always on usage of --inputbubble when compiling a composite image

* - Add a scheme to perform public signing with a PublicKeyToken to a composite of the composite image if required
  - Required adding a new parameter to crossgen2