CDATA support for XML

[som-snytt]

Forward port https://github.com/scala/scala/commit/f428cc6d94bbfee6ba3f7a956d0eee7126d785af Forward port https://github.com/scala/scala/commit/85136e3f2591f0bf22d3845ecc83081a0b6c4aa4 Forward port https://github.com/scala/scala/commit/4df81aab315e587d9c7e319c7a2ece0f0f6fbaf3

The biggest diff is for the CDATA support.

Fixes end of literal on windows, and start of literal includes open bracket.

The position fix is at https://github.com/lampepfl/dotty/pull/15635

Fixes #15574

[som-snytt]

That community build failure is quite inscrutable

hi
hi
hi
Info Provided - howdy
Info Provided - howdy
[error] Failed tests:
[error] 	org.scalatest.diagrams.DirectDiagrammedAssertionsSpec
[error] 	org.scalatest.diagrams.DiagramsSpec
Info Provided - howdy
Info Provided - howdy
[warn] In the last 240 seconds, 6.901 (2.9%) were spent in GC. [Heap: 4.62GB free of 7.14GB, max 9.78GB] Consider increasing the JVM heap using `-Xmx` or try a different collector, e.g. `-XX:+UseG1GC`, for better performance.
[warn] In the last 175 seconds, 13.245 (7.6%) were spent in GC. [Heap: 4.70GB free of 8.47GB, max 9.78GB] Consider increasing the JVM heap using `-Xmx` or try a different collector, e.g. `-XX:+UseG1GC`, for better performance.

I don't see usual test output that shows "here is the bad result and here is what was expected". Scrolling didn't tell me.

I can run sbt test for scalatest but it's not obvious how to ask it to build against my local version.

For the PR, I had to publishLocal and bump the version in the sample repo.

[som-snytt]

Because I don't understand the possibly broken community build output, I'll go ahead and forward port those other fixes.

[som-snytt]

I don't know if I can request validation of the first commit. Scala 2 validation per commit makes it obvious what incurs the failure.