Disallow attaching files from our own EmailAttachmentProvider.

This is to backport a security fix reported in b/71814449 and
b/72569023. Fix is using the same approach as b/27308057, which is to
prevent Compose from accepting URIs with our own email attachment
provider.

Bug: b/71814449
Change-Id: Idcc002b94bcea913383b54bcf1dc5c3e1d254ded
(cherry picked from commit 44a5db2dc0ace4d360699c11c27d5c10b43ad628)