[stdlib] Pin scala3 files before merging the full history (#23517)

Before merging the history of the scala 2 library with Dotty, we first
pin the set of files to be compiled for now.
This will change in 3.8.0 when we bundle all the files of the scala 3
library in the same jar and drop the dependency to scala2 stdlib

[test_non_bootstrapped]

Author: hamzaremmal