Prevent AAPT2 from versioning <set> tags

In AAPT, if --no-version-vectors is added and an XML file is a vector, it prevents the entire XML's contents, including children attributes, from being split by version for compat.

In AAPT2, each element is checked individually, and so "set" has to be ignored manually.

Bug: 111056281

Test: Compiled avd_progress_indeterminate_horizontal.xml linked in bug

Change-Id: I20a7888f36cf5923b6dd8e3b701243c74f8d421b