[test] Rename all module.map files to module.modulemap

`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

test/SourceKit/Inputs/libIDE-mock-sdk/FooHelper.framework/Modules/module.modulemap

@@ -0,0 +1,12 @@
+framework module FooHelper {
+  umbrella header "FooHelper.h"
+
+  framework module FooHelperSub {
+    umbrella header "FooHelperSub.h"
+  }
+
+  explicit module FooHelperExplicit {
+    header "FooHelperExplicit.h"
+  }
+}
+