REPL: Use event to orchestrate precompilation script

[IanButterworth]

Fixes #60239

• Make building the stdlibs throw if they error(!).. I believe they used to but regressed somewhere.. Make stdlib precompile failures throw #60308
• Add a prompt Base.event to REPL and use it to orchestrate the precompile script, rather than awkwardly reading for prompt prints

[Keno]

What was the actual reason that the precompile script failed? I actually generally liked the reading of the tty since it most closely replicated the actual user experience.

[IanButterworth]

Some syncing issue. I couldn't figure it out and got fed up with the text matching approach.

Checking the output text for test purposes sounds fair but for precompile purposes this seems more robust and maybe faster?

[IanButterworth]

It'd be good to get the strict change in and backported. @Keno I'll split that out if the other changes aren't persuasive.

[Keno]

Yeah, let's do that. I'm not sure I have a particularly strong objection to the condition, it just seems iffy to have a special case there in something that is supposed to emulate actual usage. I can't think of a real practical issue though.

[IanButterworth]

Perhaps a 2nd opinion would help. @vtjnash?

[xal-0]

👍 to this change, as well as keeping the debug output around by default. Long-term I'd like to make the REPL static enough to be precompiled entirely with precompile statements for public functions, but that needs #60259 to be merged, as well as a fix for #60303.

[IanButterworth]

as well as keeping the debug output around by default

This also makes debugging a lot easier by printing all the debug stuff on error.

[IanButterworth]

Thanks. I'll go ahead to get builds green again.