Add Compile to service_slim and pub-sub pattern

[alfonsogarciacaro]

Changes discussed in the following PRs:

• Precompile files fable-compiler/Fable#2659
• Pub-sub pattern for F#-Fable compilation fable-compiler/Fable#2676

Strange, I thought I had the same commits from dotnet/fsharp in my fork than in yours @ncave, but maybe I rebased it again later. In any case, the only commit that matters is the last one, so you can cherry-pick it if you prefer 👍

[ncave]

@alfonsogarciacaro I cherry-picked your commit as you suggested, so closing this PR.

Sounds like a great improvement, thank you!
Some minor comments:

• Technically you don't need to pass in a subscriber callback if you process files one by one by always passing lastFile to checker.ParseAndCheckProject. But it's fine, it works either way.
• Perhaps you can rebase/rebranch from my fork just so that we're on the same page and don't need to cherry-pick.

[alfonsogarciacaro]

Ah, you're right! For some reason I didn't think of that possibility 😅 There would be some overhead as we have to hit the cache many more times (and maybe some more extra work to initialize and create the project results). Probably it won't be noticeable but if you're ok with the callback, we can leave it as is for now 👍 I will rebranch from your fork.