Switch to ts-go for compiling built-in extensions

[mjbvz]

Let's see if we can use tsgo to compile our built-in extensions. It can compile our extensions pretty fast (at most one second per extension) which means we can remove much of our custom compiling logic for tsb and transpileOnly, at least for extensions

One small road bump is that tsgo currently can't be used as a library so we'll have to call it from the command line

Work towards this:

• Switching to normal decorators: 2baf1b4
• Isolated compiling of extensions: #271171

[mjbvz]

Work in progress branch: dev/ts-go-ext-compile

Still blocked by microsoft/typescript-go#914 since our runtimes don't support the stage 3 decorators yet

cc @rebornix @jrieken @bpasero @alexdima for awareness. Using ts-go, it takes around 6 second to compile and type check all of our built-in extensions