Create a synthetic Bazel workspace.

It's under out/soong/workspace and is a symlink forest that merges BUILD
files generated by bp2build and the source tree.

bazel-* symlinks and $OUTDIR are currently ignored.

Test: Presubmits.
Change-Id: If14df23bd0f6a6f2d7d1140f95213f2aee66d652
diff --git a/bp2build/conversion_test.go b/bp2build/conversion_test.go
index 9fd6817..262a488 100644
--- a/bp2build/conversion_test.go
+++ b/bp2build/conversion_test.go
@@ -19,14 +19,14 @@
 	"testing"
 )
 
-type filepath struct {
+type bazelFilepath struct {
 	dir      string
 	basename string
 }
 
 func TestCreateBazelFiles_QueryView_AddsTopLevelFiles(t *testing.T) {
 	files := CreateBazelFiles(map[string]RuleShim{}, map[string]BazelTargets{}, QueryView)
-	expectedFilePaths := []filepath{
+	expectedFilePaths := []bazelFilepath{
 		{
 			dir:      "",
 			basename: "BUILD",