Update Embedding-Build-Tools.md to reflect the moving of GraalPyResources to graalpy-extensions

[simonis]

docs/user/Embedding-Build-Tools.md still references GraalPyResources from the https://github.com/oracle/graalpython repository where it doesn't exist any more after Remove projects moved to github.com/oracle/graalpy-extensions moved it to it's own repository at https://github.com/oracle/graalpy-extensions.

Update the doc with the new, correct links and mention that GraalPyResources now lives in it's own, independent graalpy-extensions project.