Separate the files of bp2build and soong_build.

The following files are forked:

- build-globs.ninja
- The glob list files
- .d files for the glob list files
- The output file (build.ninja or the bp2build marker file)

This makes bp2build and soong_build not overwrite each other's files
they need for proper incrementality.

Test: Presubmits.

Change-Id: I69d192cbd36ecd9677f46f3fa095dfce6f872227

ui/build/config.go

@@ -739,6 +739,14 @@ func (c *configImpl) SoongOutDir() string {
 	return filepath.Join(c.OutDir(), "soong")
 }
 
+func (c *configImpl) MainNinjaFile() string {
+	return shared.JoinPath(c.SoongOutDir(), "build.ninja")
+}
+
+func (c *configImpl) Bp2BuildMarkerFile() string {
+	return shared.JoinPath(c.SoongOutDir(), ".bootstrap/bp2build_workspace_marker")
+}
+
 func (c *configImpl) TempDir() string {
 	return shared.TempDirForOutDir(c.SoongOutDir())
 }