chore: rename bundler to Bundler for consistency

While the configuration options are not case-sensitive, it is good to
keep the casing consistent.
The JSON schema at https://json.schemastore.org/tsconfig uses `Bundler`,
so we should use the same casing.

tsconfig.json

@@ -13,7 +13,7 @@
 
     // We expect users to use bundlers.
     // So here we enable some resolution features that are only available in bundlers.
-    "moduleResolution": "bundler",
+    "moduleResolution": "Bundler",
     "resolveJsonModule": true,
     "allowImportingTsExtensions": true,
     // Even files without `import` or `export` are treated as modules.