`module.map` as a module map name has been discouraged since 2014, and
Clang will soon warn on its usage. This patch renames all instances of
`module.map` in the Swift tests to `module.modulemap` in preparation
for this change to Clang.
rdar://106123303
`#import` has target dependent behaviour. Rather than enabling ObjC
interop, switch to `#include` with include guards. This permits the IDE
tests to fully pass on Windows.
Because we don't want FooModule.#^A^# to show completion results for other
clang modules, global completion cache was replaced with a per-module cache.
Swift SVN r6951
