Fix ManifestMerger issues

Set LOCAL_MIN_SDK_VERSION in aapt2 integration test libraries so that
the build system doesn't raise the minSdkVersion value specified in
the manifest, which causes ManifestMerger to error when trying to
merge it into a package that specifies a lower minSdkVersion.

Bug: 78447299
Test: m java
Change-Id: If5d4f97bb2d8a503bd3c20f2ea8aea2519c51e85