Allow exporting bazel mixed build allowlists to simple text files

So that they the allowlists can be read from build_mainline_modules_bundles.sh.

Bug: 262302253
Test: m out/soong/bazel_prod_mixed_builds_enabled_list.txt out/soong/bazel_staging_mixed_builds_enabled_list.txt && cat out/soong/bazel_prod_mixed_builds_enabled_list.txt && echo && cat out/soong/bazel_staging_mixed_builds_enabled_list.txt
Change-Id: Id5f89ebb651a52dc5368681a20d6183703e05bd4
diff --git a/bp2build/conversion_test.go b/bp2build/conversion_test.go
index 8de2f83..dfc7f0b 100644
--- a/bp2build/conversion_test.go
+++ b/bp2build/conversion_test.go
@@ -147,6 +147,14 @@
 			dir:      "api_levels",
 			basename: "api_levels.bzl",
 		},
+		{
+			dir:      "allowlists",
+			basename: "mixed_build_prod_allowlist.txt",
+		},
+		{
+			dir:      "allowlists",
+			basename: "mixed_build_staging_allowlist.txt",
+		},
 	}
 
 	if len(files) != len(expectedFilePaths) {