Reland "Use cp instead of install for ndk_headers"

This relands aosp/3026027 with fixes for ndk_library. ndk_library
uses ctx.InstallFile to copy the stubs from an intermediate dir to
out/soong/ndk/sysroot/. The copy rule was created in
out/soong/installs-<product>.mk. This would cause issues when soong_ui
is run in `--soong-only` mode

To fix this, the cp rule is created entirely in soong. The stub library
is marked uninstallable to prevent creation of duplicate rules when
`--soong-only` mode is not used

Test: presubmits
Test: lunch ndk-trunk_staging-userdebug &&
ALLOW_MISSING_DEPENDENCIES=true build/soong/soong_ui.bash --soong-only
out/soong/ndk.timestamp

Change-Id: I6f8b87d88d8ca5ec9a3327e1f11e9aa654f8cdce