Export apex_available_baseline to soong_injection

So that it can be used in the bazel implementation.

Bug: 268006095
Test: m nothing, check that it's in out/soong/soong_injection
Change-Id: I1520dd874076dee7fa083648d0790b060d658e5a
diff --git a/bp2build/conversion.go b/bp2build/conversion.go
index 5b3e19f..73df675 100644
--- a/bp2build/conversion.go
+++ b/bp2build/conversion.go
@@ -22,7 +22,7 @@
 }
 
 // PRIVATE: Use CreateSoongInjectionDirFiles instead
-func soongInjectionFiles(cfg android.Config, metrics CodegenMetrics) []BazelFile {
+func soongInjectionFiles(cfg android.Config, metrics CodegenMetrics) ([]BazelFile, error) {
 	var files []BazelFile
 
 	files = append(files, newFile("android", GeneratedBuildFileName, "")) // Creates a //cc_toolchain package.
@@ -36,7 +36,11 @@
 	files = append(files, newFile("java_toolchain", "constants.bzl", java_config.BazelJavaToolchainVars(cfg)))
 
 	files = append(files, newFile("apex_toolchain", GeneratedBuildFileName, "")) // Creates a //apex_toolchain package.
-	files = append(files, newFile("apex_toolchain", "constants.bzl", apex.BazelApexToolchainVars()))
+	apexToolchainVars, err := apex.BazelApexToolchainVars()
+	if err != nil {
+		return nil, err
+	}
+	files = append(files, newFile("apex_toolchain", "constants.bzl", apexToolchainVars))
 
 	files = append(files, newFile("metrics", "converted_modules.txt", strings.Join(metrics.Serialize().ConvertedModules, "\n")))
 
@@ -52,7 +56,7 @@
 
 	apiLevelsContent, err := json.Marshal(android.GetApiLevelsMap(cfg))
 	if err != nil {
-		panic(err)
+		return nil, err
 	}
 	files = append(files, newFile("api_levels", GeneratedBuildFileName, `exports_files(["api_levels.json"])`))
 	files = append(files, newFile("api_levels", "api_levels.json", string(apiLevelsContent)))
@@ -64,7 +68,7 @@
 	files = append(files, newFile("allowlists", "mixed_build_prod_allowlist.txt", strings.Join(android.GetBazelEnabledModules(android.BazelProdMode), "\n")+"\n"))
 	files = append(files, newFile("allowlists", "mixed_build_staging_allowlist.txt", strings.Join(android.GetBazelEnabledModules(android.BazelStagingMode), "\n")+"\n"))
 
-	return files
+	return files, nil
 }
 
 func CreateBazelFiles(