Expose '--force-sparse-encoding' flag for 'optimize' and 'convert' commands.

This allows to use sparse encoding for APKs that do not specify minSdk
version inside. This is common for split APKs generated by bundletool
when Android App Bundle (AAB) is split into multiple APKs.

Bug: b/223394605
Test: TableFlattener_test
Change-Id: I2a99a611f855cffbcea20018d869e1eb54d1b3d5