To manage the generation step, introduce cmGeneratorFileSet and
cmGeneratorFileSets classes.
These reorganizations of the code are done in preparation of the
implementation of SOURCES file set type as well as user's file set types.
Issues: #27550, #27383
Run the `clang-format.bash` script to update all our C and C++ code to a
new style defined by `.clang-format`, now with "east const" enforcement.
Use `clang-format` version 18.
* If you reached this commit for a line in `git blame`, re-run the blame
operation starting at the parent of this commit to see older history
for the content.
* See the parent commit for instructions to rebase a change across this
style transition commit.
Issue: #26123