Handle activation conflicts for `[patch]` sources
This commit updates the resolver to ensure that it recognizes conflicts
when `[patch]` is used to augment an older version of what's already in
a source, for example. Previously the deduplication based on
semver-compatible versions didn't actually work when `[patch]` was used.
This meant that when you used `[patch]` it might not transitively affect
the entire crate graph, instead just giving you a version of a
dependency and everyone else. This violates the intention of `[patch]`!
The fix here is to catch this use case happening, when a `Dependency`
source specification mismatches an activated package we need to list a
second activation in the resolver to prevent major versions from being
selected from both the original source as well as the source of the id.
Closes#7117
0dd7c508d0