Recursively enable dependencies' dependencies

[madsmtm]

When requesting the block2 feature in e.g. objc2-cloud-kit, the block2 feature of objc2-foundation is not enabled, which leads to build errors, see this.

So instead of the feature flags being:

block2 = ["dep:block2"]
objc2-core-location = ["dep:objc2-core-location"]

They should be:

block2 = ["dep:block2", "objc2-foundation/block2", "objc2-core-location?/block2"]
objc2-core-location = ["dep:objc2-core-location"]