Specifying these three values in Gradle files is common practice.

There are a couple spots in our build pipeline that would benefit from knowing minSdkVeriosion in GN:
* When dexing,
* When proguarding (with r8)


Additionally specifying targetSdkVersion and packageName in GN would allow us to stop using jinja templates for several simple AndroidManfest.xml files. E.g.:
 * https://cs.chromium.org/chromium/src/chrome/android/javatests/AndroidManifest.xml
 * https://cs.chromium.org/chromium/src/chrome/android/modules/vr/AndroidManifest.xml
 * https://cs.chromium.org/chromium/src/testing/android/empty_apk/AndroidManifest.xml

List of all manifests that are templates (~1/4 of them are "simple"):
https://cs.chromium.org/search/?q=file:androidmanifest.xml+%5C%7B%5C%7B&sq=package:chromium&type=cs


minSdkVersion in GN is being added here:
https://chromium-review.googlesource.com/c/chromium/src/+/1258059

Note that "aapt2 link" supports setting these values in the manifest via:
--min-sdk-version
--target-sdk-version
--rename-manifest-package
--rename-instrumentation-target-package


When going ahead with this, we should set a build-wide default minSdkVersion and targetSdkVersion so that these values are always present for targets. It should be an error for an AndroidManifest.xml to have a <uses-sdk> tag in it, so that we don't need to enforce that it matches the GN value.