Verification

• I have updated Composer to the most recent stable release (composer self-update)
• I have updated Composer Patches to the most recent stable release (composer update cweagans/composer-patches)
• I am using one of the supported PHP versions (8.0+)
• I have searched existing issues and discussions for my idea.

Is your feature request related to a problem?

Yes, a patch will not be applied from one of the packages I'm installing (my own package).

Setup:

Root project
|_ dep 1 (required by root, containing patch)
|_ dep 2 (required by dep 1, should be patched by dep 1) 

issue 1
When dependency 1 uses an external patch file the patches are not detected and thus never applied.
gatherPatches only searches for the patches key.

issue 2
When switching to the patches configuration the patch will be found but when it's not an url but a local path e.g. patches/my-patch.patch an error occurs because paths are only resolved relative to the root directory.
My current workaround is adding a symlink in my root project.

Describe your proposed solution(s)

Add support for the patches-file configuration for dependencies and use dependency/package root that defines a patch to resolve relative paths for patches.

Describe alternatives

Add documentation that an external patch file only works for root projects (although this does not make a lot of sense to me).
To resolve the relative path issue an alternative could be to copy all gathered patches into a temp dir.

Additional context

No response