Allow calling ctx.DistForGoal from Singletons

Right now singletons have to dist files in either in MakeVars providers.
Allow dist from GenerateBuildActions so that we can further remove our
reliance on make.

Bug: 395184523
Test: m nothing --no-skip-soong-tests
Change-Id: Ie3004c2b038b45754279dfadcb7f7455ae740136