Fix Xcode 11.3.1 detection in an Xcode workspace
Fix Xcode 11.3.1 detection in an Xcode workspace

When using a Tulsi-generated project by itself in Xcode 11.3.1, Xcode
sets XCODE_VERSION_ACTUAL to 1131, which Tulsi parses correctly to get
the version 11.3.1.

But when used in an Xcode workspace, Xcode sets XCODE_VERSION_ACTUAL
to 1130, leading to Tulsi parsing 11.3 as the version, and later
attempts to use a non-existing version of Xcode to build, which results
in an error.

Fix by ignoring XCODE_VERSION_ACTUAL because it's unreliable; instead,
parse Xcode's version.plist to read the 'CFBundleShortVersionString'
entry, which seems to return correct results.

Caveat: this implementation uses plistlib, which has a slightly
different API in python2 and python3. This change uses the python2 API,
and will need to be updated to work with python3 in the future.
PiperOrigin-RevId: 315886285

bazelbuild/tulsi,bazelbuild/tulsi,bazelbuild/tulsi,bazelbuild/tulsi,bazelbuild/tulsi,bazelbuild/tulsi