Remove com.android.internal{.util} from generated documentation.

com.android.internal.* is meant to be hidden from documentation,
but most of it is erroneously not hidden via @hide or -hidePackage
directives; why documentation is currently generated for Predicate
but not other classes from com.android.internal.util, and why some
but not all classes from that package show up in package-level
documentation (package-summary.html), is not currently understood.

There appears to be a behavior difference between OpenJDK 8 and
OpenJDK 9's javadoc that results in additional classes showing up
in package-summary.html. This CL fixes this by adding -hidePackage
directives for com.android.internal{.util}; other sub-packages of
com.android.internal do not currently show up in documentation and
are not touched by this CL.

Test: Patched this CL into the internal-master branch and ran:
      USE_R8=true EXPERIMENTAL_USE_OPENJDK9=true make offline-sdk-docs
      Checked that this removes all documentation for com.*
      (com.android.internal.util was the only com.* package for which
      documentation was previously generated).
      In other words: Before this CL, [1] existed, but after
      this CL, the entire directory subtree [2] does not exist.
Test: Checked that Predicate was already missing from stubs before this
      CL. In other words, [3] already did not exist before this CL.

[1] out/target/common/docs/offline-sdk/reference/com/android/internal/util/Predicate.html
[2] out/target/common/docs/offline-sdk/reference/com
[3] out/target/common/obj/JAVA_LIBRARIES/android_system_stubs_current_intermediates/classes/com

Bug: 69736344
Bug: 69736236

(cherry picked from commit 97bb6cf3)

Merged-In: Ic9757f4966f54092aac0191896581fa4222cc634
Change-Id: Ic9757f4966f54092aac0191896581fa4222cc634