File size seal for memory mapped region

When using memfd for cross process communication, we always need to seal
the file size, otherwise remote process and shrink the size we memory
mapped and thus crash the originate process causing a DoS

Bug: 294609150
Test: Build
Ignore-AOSP-First: security
(cherry picked from commit 3d9f1e3b)
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:f2c1d9d28083fdcba53f346bba5289e72bc4be49)
Merged-In: Ibc263c4f78df897e884378e3d984a188ca8772c7
Change-Id: Ibc263c4f78df897e884378e3d984a188ca8772c7