Make the bundler tests use the API by default in most cases (#22646)

### What does this PR do?

This branch:
> Ran 1600 tests across 46 files. [63.24s]

Main:
> Ran 1600 tests across 46 files. [137.05s]

This makes the bundler tests run about 60 seconds faster 

### How did you verify your code works?

test/bundler/bundler_compile.test.ts

@@ -106,6 +106,7 @@ describe("bundler", () => {
     run: { stdout: "Hello, world!" },
   });
   itBundled("compile/WorkerRelativePathNoExtension", {
+    backend: "cli",
     compile: true,
     files: {
       "/entry.ts": /* js */ `
@@ -125,6 +126,7 @@ describe("bundler", () => {
     run: { stdout: "Hello, world!\nWorker loaded!\n", file: "dist/out", setCwd: true },
   });
   itBundled("compile/WorkerRelativePathTSExtension", {
+    backend: "cli",
     compile: true,
     files: {
       "/entry.ts": /* js */ `
@@ -143,6 +145,7 @@ describe("bundler", () => {
     run: { stdout: "Hello, world!\nWorker loaded!\n", file: "dist/out", setCwd: true },
   });
   itBundled("compile/WorkerRelativePathTSExtensionBytecode", {
+    backend: "cli",
     compile: true,
     bytecode: true,
     files: {
@@ -558,6 +561,7 @@ describe("bundler", () => {
   });
   itBundled("compile/ImportMetaMain", {
     compile: true,
+    backend: "cli",
     files: {
       "/entry.ts": /* js */ `
         // test toString on function to observe what the inlined value was

test/bundler/bundler_edgecase.test.ts

@@ -274,6 +274,7 @@ describe("bundler", () => {
       "/entry.js": /* js */ `console.log(1)`,
     },
     outdir: "/out",
+    backend: "cli",
     loader: {
       ".cool": "wtf",
     },
@@ -2071,6 +2072,7 @@ describe("bundler", () => {
   });
 
   itBundled("edgecase/OutWithTwoFiles", {
+    backend: "cli",
     files: {
       "/entry.ts": `
         import index from './index.html' with { type: 'file' }

test/bundler/bundler_footer.test.ts

@@ -4,6 +4,7 @@ import { itBundled } from "./expectBundled";
 describe("bundler", () => {
   itBundled("footer/CommentFooter", {
     footer: "// developed with love in SF",
+    backend: "cli",
     files: {
       "/a.js": `console.log("Hello, world!")`,
     },
@@ -16,6 +17,7 @@ describe("bundler", () => {
  * This is copyright of [...] ${new Date().getFullYear()}
  * do not redistribute without consent of [...]
 */`,
+    backend: "cli",
     files: {
       "index.js": `console.log("Hello, world!")`,
     },

test/bundler/bundler_regressions.test.ts

@@ -216,6 +216,7 @@ describe("bundler", () => {
   });
 
   itBundled("regression/WindowsBackslashAssertion1#9974", {
+    backend: "cli",
     files: {
       "/test/entry.ts": `
         import { loadFonts } from "../base";

test/bundler/compile-argv.test.ts

@@ -7,6 +7,7 @@ describe("bundler", () => {
     compile: {
       execArgv: ["--title=CompileExecArgvDualBehavior", "--smol"],
     },
+    backend: "cli",
     files: {
       "/entry.ts": /* js */ `
         // Test that --compile-exec-argv both processes flags AND populates execArgv
@@ -52,6 +53,7 @@ describe("bundler", () => {
     compile: {
       execArgv: ["--user-agent=test-agent", "--smol"],
     },
+    backend: "cli",
     files: {
       "/entry.ts": /* js */ `
         // Test that compile-exec-argv options don't appear in process.argv
@@ -115,6 +117,7 @@ describe("bundler", () => {
     compile: {
       execArgv: ["--user-agent=test-agent", "--smol"],
     },
+    backend: "cli",
     files: {
       "/entry.ts": /* js */ `
         // Test that user arguments are properly included when exec argv is present

test/bundler/esbuild/dce.test.ts

@@ -1241,6 +1241,7 @@ describe("bundler", () => {
       },
       minifyWhitespace: minify,
       emitDCEAnnotations: emitDCEAnnotations,
+      backend: "cli",
       onAfterBundle(api) {
         const code = api.readFile("/out.js");
         expect(code).not.toContain("_yes"); // should not contain any *_yes variables

test/bundler/expectBundled.ts

@@ -572,7 +572,22 @@ function expectBundled(
 
   return (async () => {
     if (!backend) {
-      backend = plugins !== undefined ? "api" : "cli";
+      backend =
+        dotenv ||
+        jsx.factory ||
+        jsx.fragment ||
+        jsx.runtime ||
+        jsx.importSource ||
+        typeof production !== "undefined" ||
+        bundling === false ||
+        (run && target === "node") ||
+        emitDCEAnnotations ||
+        bundleWarnings ||
+        env ||
+        run?.validate ||
+        define
+          ? "cli"
+          : "api";
     }
 
     let root = path.join(
@@ -1107,7 +1122,13 @@ for (const [key, blob] of build.outputs) {
         configRef = buildConfig;
         let build: BuildOutput;
         try {
-          build = await Bun.build(buildConfig);
+          const cwd = process.cwd();
+          process.chdir(root);
+          try {
+            build = await Bun.build(buildConfig);
+          } finally {
+            process.chdir(cwd);
+          }
         } catch (e) {
           if (e instanceof AggregateError) {
             build = {