Fully support make-style `.d` dependencies file output by making
following improvements:
* All correct dependency file render when cache hit for a different
output file location. The dependency file should list the correct
output path, not the stale output path for the initial compilation
* When enable a path prefix mapper to canonicalize the path, the
dependency file should render the input file correctly as the input
file path on disk.
rdar://132250067
Avoid path encoding difference (for example, real_path vs. path from
symlink) by eliminating the path from cache key. Cache key is now
encoded with the index of the input file from all the input files from
the command-line, reguardless if those inputs will produce output or
not. This is to ensure stable ordering even the batching is different.
Add a new cache computation API that is preferred for using input index
directly. Old API for cache key is deprecated but still updated to
fallback to real_path comparsion if needed.
As a result of swift scan API change, rename the feature in JSON file to
avoid version confusion between swift-driver and libSwiftScan.
rdar://119387650
Update swift cache key computation mechanism from one cache key per
output, to one cache key per primary input file (for all outputs that
associated with that input).
The new schema allows fewer cache lookups while still preserving most of
the flexibility for batch mode and incremental mode.
