potentially fix monaco editor build bug

[jwunderl]

I think this will fix the bug that rare build issue that caused microsoft/pxt-arcade#6077. The bits leading me to think that are that it's pointing at /codicons/codicon/codicon.ttf while grabbing the editor.css, which matches the error we got

and that inlineCodiconFont's job is to replace that relative path with an inline font - so the replace in that fn is not being applied to the end result (it's just a few lines above this change). It's a bit hard to induce the bug, but I think it's a race condition with the fs.readFileSync vs gulp.src in inlineCodiconFont and copyMonacoEditor functions, where it normally runs fine but very rare fs lag causes inlineCodiconFont to get applied first then overwritten. I guess I can try inducing it by throwing in a for (let i = 0; i < 10000000000; i++) {i ++} or something in copyMonacoEditor?

I did a local serve and uploadtrg and both have icons as expected, it also just makes sense that the mutation of the file should not be running parallel to copying the file~

(I also kinda wonder if this was the cause for comment on line 504 -- it's fetching from the cdn relative to the .css file, but the path at the end is just for reference / the hash is what matters, so it was always pulling in the css and trying to use it as ttf. Probably the right fix though as would maybe be a bit of a headache to replace in the right cdn path)