AOSP/Email - bug fix: do not allow composing message with hidden private data...

AOSP/Email - bug fix: do not allow composing message with hidden private data attachments - Switch intent filtering to be blacklist based rather than whitelist based.

+ Blacklist only EXTRA_IN_REFERENCE_TO_MESSAGE_URI.
+ Undoing some of the changes from https://android-review.googlesource.com/c/platform/packages/apps/Email/+/961354/
+ Ported/merged this change from CL: cl/235253805 (to match the internal version - ComposeActivityGmailExternal.java)

Bug: 127320867

Test: manual - Ran the following tests on Pixel phone. Tested the email UI.

$ make -j 40
$ make Email -j
$ make UnifiedEmailTests -j
$ make EmailTests -j

  -rw-r--r-- 1 rtenneti primarygroup 6356400 Oct  1 12:07 out/target/product/marlin/testcases/Email/arm64/Email.apk
  -rw-r--r-- 1 rtenneti primarygroup 389599 Oct  1 12:11 out/target/product/marlin/testcases/EmailTests/arm64/EmailTests.apk

$ adb install -r -d -g out/target/product/marlin/testcases/Email/arm64/Email.apk
$ adb install -r -d -g out/target/product/marlin/testcases/EmailTests/arm64/EmailTests.apk

$ adb shell am instrument -w com.android.email.tests
  Time: 2.739
  OK (157 tests)

$ atest EmailTests
  Summary
  -------
  EmailTests: Passed: 157, Failed: 0, Ignored: 0, Assumption Failed: 0

  All tests passed!

Change-Id: I5a397b61827b82502d26da2496831011956c868a