Implement --file-names-only

[jtdavis777]

Fixes #8784

Adds (my best attempt at) a minimally invasive implementation of --file-names-only.

Note that this version prints every file the program attempts to write -- during testing I found #8787 where python tries and silently fails to make a file. Other languages may have the same problem.

[jtdavis777]

[jtdavis777]

@aardappel thanks for the thorough review! I can go back and not be so heavy handed with my cleanup.

Most of the file manager code that I cleaned up was brought in #7821, which was never used in our repo. I respect the callout that other people ingesting our code base may take advantage of them though.

[aardappel]

Ok, I'd agree any code that comes from an incomplete/non-functional PR that was merged is probably good to delete if not used in your fix. Still would prefer to minimize renames.

[jtdavis777]

seems like a decent middle ground. I'll compare with the original and roll back to being less aggressive, and will put back the helper functions.

[aardappel]

looks like the way the fuzzer builds needs updating

CMake Error at CMakeLists.txt:220 (add_executable): Cannot find source file: /src/flatbuffers/src/file_name_saving_file_manager.cpp``` 

[fliiiix]

@jtdavis777 some docs for this feature would be nice