Clean up esbuilding of extensions

- Make sure we still always type check using `tsgo --noEmit`
- Align names of esbuild files
- Convert all esbuild files to typescript. We use the `.mts` extension to avoid annoying node warnings about using pacakges

extensions/markdown-language-features/tsconfig.browser.json

@@ -3,5 +3,8 @@
 	"compilerOptions": {},
 	"exclude": [
 		"./src/test/**"
+	],
+	"files": [
+		"./src/extension.browser.ts"
 	]
 }