Each conversion required defining a separate mutator, which will each
operate on _all_ modules and requires each to repeat checks whether the
mutator should operator. Instead, we introduce a single mutator and
modules can define a ConvertWithBp2build to implement bp2build
conversion for that module.
Test: bp2build.sh
Bug: 183079158
Change-Id: I99d4b51f441c2903879092c5b56313d606d4338d
Moves to specifying attributes as a map, such at it is possible to add
additional attributes conditionally. This is in particular useful once
supporting the `enabled` property which will add
`target_compatible_with`
Test: go test soong tests
Change-Id: Iade8eed1ce3acb1d1712a9ee3119d9ae59675624
