Improve the version/flags extract from interface file by moving away
from using Regex and limiting the search to the beginning of the file.
Switch away from Regex will give 5-10% improvement in time and
instruction counts, and limiting the search lines can save a lot of time
if the swiftinterface is large. For example, the extract time for Swift
stdlib is 10x faster after the patch.
Current strategey for limiting the line to search is by only parsing the
first comment block.
We already have something called "module interfaces" -- it's the
generated interface view that you can see in Xcode, the interface
that's meant for developers using a library. Of course, that's also a
textual format. To reduce confusion, rename the new module stability
feature to "parseable [module] interfaces".
The presence of a deinitializer will eventually indicate whether a
class's deinitializer is non-trivial for non-resilient modules.
Also improve recovery for normal source files for various bad ways
of declaring a deinitializer.
