Support extra tags in system image prop templates

Add support for ${EXTRA_SYSTEM_IMAGE_TAGS} and
${EXTRA_SYSTEM_IMAGE_TAG_DISPLAY} in sdk-preprocess-files.mk.

This allows products to conditionally append tags to system image
source.properties without hardcoding them in shared templates.

Bug: 505483910
Bug: 496979825
Flag: build.RELEASE_PACKAGE_GLASSES_EMULATOR_ENABLED
Test: Verify source.properties generation with and without tags
Cherrypick-From: https://googleplex-android-review.googlesource.com/q/commit:2472c647fee4ad1253bfc9ba263eaae04da92f05
Merged-In: I9f5911782862ca4284557f31d704649b25507994
Change-Id: I9f5911782862ca4284557f31d704649b25507994