* Update bpdocs to filter nested properties by tag
Prior to this change nested properties tagged with `blueprint:"mutated"`
are erroneously included in documentation, this corrects that behavior
and adds testing to verify.
Tested: go test bpdocs tests
Change-Id: I822c9a98276634d2f584d8709e83003824cdffd5
This change fixes a bug where the `blueprint:mutated` tag was ignored
when used for struct or interface properties. It also fixes a dormant
ExcludeByTag func bug.
Test: m soong_docs, properties_test.go, bpdoc_test.go
Change-Id: I926de2aa203ec552ced897174e9b78e817701a7d