Improve and standardize output to stderr

[Electroid]

Our current output to stderr is usually hard to read. There's also no standard format, so it's all over the place depending on the error and context. If we compare it to the output that esbuild prints, it's hard to compare.

wrangler, when you upload a script that throws an error on startup:

esbuild, when you try to upload a script with syntax errors:

The format that esbuild uses is actually really nice, maybe we could adopt a similar (or same) format? Here's the algorithm it uses to generate that format.

Edit: It looks like esbuild actually exposes an API to format text in its format. We could use that.

[threepointone]

#734 (comment)

[petebacondarwin]

#848 actually implements the esbuild formatting for errors and warnings. So I think we can close this one.