Travis-CI: build and test on Windows

[SethTisue]

EXPERIMENT.

if this can be made to work, we could get rid of our Windows stuff on Jenkins. (that stuff is currently chugging along fine, but it is historically fragile, difficult to troubleshoot, difficult to recreate)

yes, in the long run, GitHub Actions seems like a likelier path forward. but for now we are on Travis-CI, and also I know Travis-CI but I don't know GitHub Actions yet. so if I can get this running without it turning into a big time sink, win.

if a volunteer would like to PR a GitHub Actions alternative to this, that would be welcome! we can explore that path too.

[SethTisue]

the first problem is that we import: scala/scala-dev:travis/default.yml which has a before_install that tries to install Java using sdkman, which fails with Please install zip on your system using your favourite package manager

one path forward would be install zip, as it asks. we're going to want to do the Windows testing on JDK 8 and 11 minimum, and perhaps 15, 16, and/or 17, too, so we'll need a way of getting different JDKs.

or, looking at the handful of other Scala OSS projects I've found that use os: windows in their .travis.yml, it looks like there's an .install-jdk-travis.sh script we can use, and it allows specifying e.g. env: JDK="adopt@1.8.0-222". I guess I'll try that since it seems likely it will just work. and if it does, then I can deal with the conflict with scala-dev:travis/default.yml

[SethTisue]

this seems rather puzzling: Invalid maximum heap size: -Xmx2G. even the 32-bit version of Java shouldn't object to that, and anyway it seems from the log that we are on 64-bit Java as hoped/expected, OpenJDK 64-Bit Server VM

I guess I'll remove our .jvmopts and press on? but yuck

[SethTisue]

For reference, on our Jenkins it takes 60-70 minutes

[SethTisue]

https://travis-ci.com/github/scala/scala/jobs/482066040 succeeded in 86 minutes

[griggt]

if a volunteer would like to PR a GitHub Actions alternative to this, that would be welcome! we can explore that path too.

I put something together real quick in #9496 as a starting point.

[SethTisue]

the -Xmx2G mystery was cleared up by @griggt at #9496 (comment)

[SethTisue]

at this point #9496 seems like a likelier path forward, so I'm going to close this. It remains here for reference if needed.