aapt2: Ensure sparse encoding isn't used on unsupported platforms

Current behavior:
- When --enable-sparse-encoding is used, sparse encode when minSdkVersion is missing or is >= 32 (S_v2)
- When --force-sparse-encoding is used, always sparse encode regardless of minSdkVersion

New behavior:
- When --enable-sparse-encoding is used, sparse encode when minSdkVersion is >= 32 (S_v2)
- When --force-sparse-encoding is used, sparse encode when minSdkVersion is missing or is >= 32 (S_v2)

Bug: 398187461
Test: build + boot on Pixel 6 Pro
Flag: EXEMPT build tool
Change-Id: Ide4e37f565107a33ecafc269ed81633e616b1a19