[CMake][NFC] Introduce component targets for proper dependency tracking
This commit introduces a CMake target for each component, adds install targets
for them, and switches build-script-impl to use the target `install-components`
for installation. Each of the targets for each component depends on each
of the individual targets and outputs that are associated with the
corresponding swift-component.
This is equivalent to what already exists, because right now install rules are
only generated for components that we want to install. Therefore, this commit
should be an NFC.
This is a resubmission (with modifications) of an earlier change. I originally
committed this but there were problems with some installation rules.