conditional zygote child heap profiling + android_internal_mallopt

On user builds, heapprofd should only be allowed to profile apps that
are either debuggable, or profileable (according to the manifest). This
change exposes extra zygote-specific knowledge to bionic, and makes the
dedicated signal handler check for the special case of being in a zygote child.

With this & the corresponding framework change, we should now be
handling the 4 combinations of:
  {java, native} x {profile_at_runtime, profile_at_startup}.

See internal go/heapprofd-java-trigger for further context.

Test: on-device unit tests (shared & static) on blueline-userdebug.
Test: flashed blueline-userdebug, confirmed that java profiling activates from startup and at runtime.
Bug: 120409382
Change-Id: Ic251afeca4324dc650ac1d4f46976b526eae692a
(cherry picked from commit 998792e2)
Merged-In: Ic251afeca4324dc650ac1d4f46976b526eae692a