Add missing soong_docs inputs

Specifically, make Android.bp.list and soong.variables explicit inputs

While this is not a comprehensive list of all inputs
of this action (as the action depends on all blueprint
files in the source tree), this is closer to the truth.

This is a rollforward CL, which was originally rolled
back, as path validation failed for when OUT_DIR was
an absolute path. Validation has now been relaxed.

Test: Manually verified ninja output, checkbuild approved validation
  for aosp-crosshatch, and manually ran frameworks/rs/build_rs.py with
  patch fix
Change-Id: I4eb0d517f57336dd54eaa4bd31f46df9e93e6da2
diff --git a/cmd/soong_build/main.go b/cmd/soong_build/main.go
index 905f206..532d9e4 100644
--- a/cmd/soong_build/main.go
+++ b/cmd/soong_build/main.go
@@ -59,7 +59,7 @@
 	ctx := android.NewContext()
 	ctx.Register()
 
-	configuration, err := android.NewConfig(srcDir, bootstrap.BuildDir)
+	configuration, err := android.NewConfig(srcDir, bootstrap.BuildDir, bootstrap.ModuleListFile)
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "%s", err)
 		os.Exit(1)