copy: drop dependency on `the_repository`

copy: drop dependency on `the_repository`

When copying a file we need to potentially adapt permissions of the new
file based on whether or not "core.shared" is enabled. Parsing this
configuration makes us implicitly depend on `the_repository`.

Refactor the code to instead require the caller to pass in a repository
so that we can remove `USE_THE_REPOSITORY_VARIABLE`.

Signed-off-by: Patrick Steinhardt <redacted>
Signed-off-by: Junio C Hamano <redacted>