ClangImporter: add support for Android API Notes

Introduce the first APINotes injection for the Android platform. This
follows the VCRuntime pattern of permitting the SDK to provide API Notes
that augment the system SDK. This adds a workaround for incorrect
nullability on the `fts_open` function in bionic. The system library
itself is fixed at:
https://android-review.googlesource.com/c/platform/bionic/+/3151616

(cherry-picked from 47f9d78)

Author: compnerd

stdlib/public/Platform/CMakeLists.txt

@@ -472,6 +472,11 @@ if("ANDROID" IN_LIST SWIFT_SDKS)
                                  COMPONENT sdk-overlay)
     endif()
   endforeach()
+
+  swift_install_in_component(FILES
+      posix_filesystem.apinotes
+    DESTINATION "share"
+    COMPONENT sdk-overlay)
 endif()
 add_custom_target(android_modulemap DEPENDS ${android_modulemap_target_list})
 set_property(TARGET android_modulemap PROPERTY FOLDER "Miscellaneous")

stdlib/public/Platform/posix_filesystem.apinotes

@@ -0,0 +1,7 @@
+---
+Name: bionic
+Functions:
+- Name: fts_open
+  Parameters:
+  - Position: 0
+    Type: "char * const _Nullable * _Nonnull"