Implement REPL replayer for Windows

[KristofferC]

Review without whitespace: https://github.com/JuliaLang/julia/pull/28608/files?w=1

After some JuliaCon hacking with @Keno, we came up with something that replays the REPL script on Windows. The trick is to fool the spawned Julia process into believing it is being started from Cygwin by giving it a named pipe with the name satisfying a certain pattern. This makes us create TTYs for the 3 standard streams instead of e.g.IOStreams.

Since we are only faking being Cygwin we need to add a small patch to the Terminal REPL code to avoid it
trying to set some settings to the terminal that we don't care about when doing precompilation generation.

Note that this PR seems to increase the time of the precompile generation while, in fact, time has only been moved from loading the Pkg precompile statements from one place to another.

I also added a "overhead" measurement to the output:

Generating precompile statements... 1076 generated in  97.362301 seconds (overhead  59.582277 seconds)

This shows how much time we "waste" by dynamically collecting precompile statements compared to having a perfect file with precompile statements available. Since this is significant, it might be worth some extra logic to have a "build mode for developers" where the previous precompile file is tried to be used and only regenerate a new one if using the old one fails. This would be a non-default setting so build bots and CI would always regenerate from scratch.

One thing that would be good to figure out is that at the end when the REPL script has been executed, calling exit() on Windows does not shut down the process, so here we just forcefully kill it. According to @vtjnash, this would happen if we have Windows is waiting for us to finish reading from a stream, but it feels like the @async block that just keeps reading from master should deal with this...

[KristofferC]

The buildbot binary for this commit is at https://julialangnightlies-s3.julialang.org/bin/winnt/x64/1.0/julia-b8b07a227b-win64.exe and performance is good.

[KristofferC]

I'll restart AV a couple of times to see that this is stable on Windows and then I plan to merge unless someone objects. Keeping the Pkg precompile stuff up to date is super annoying since there are some quite big refactorings in e.g. the Pkg REPL code.