Added 3.4.2 support in a fairly formulaic fashion

[Ichoran]

Added 3.4.2 to targets in a fairly straightforward, formulaic fashion. 3.4.0 and 3.4.1, for good reason, fail to parse $ as a class file, but a temporary ad-hoc workaround was added in 3.4.2, so this needn't block 3.4 support for now. Reliance on object $ still needs to be fixed in Ammonite.

Several internals changes required fixes also; I used the most obvious solution (e.g. if Y extends X and Y is now private, use X instead), but someone who knows more might want to read it over.

Tests pass on my machine for 3.3 and 3.4.2 (under Java 21).

If accepted, this patch would supersede #1394

[Ichoran]

If it works, this should complete #1425

[lihaoyi]

@Ichoran how much of the stuff in the 3.4.2+/ folder really needs to be duplicated? I wonder if it actually involves a widespread change to the relevant code, or whether we just need to duplicate a few helper functions and the rest of the code can remain shared for easier maintainability

[Ichoran]

@lihaoyi - Yeah, I wasn't entirely happy with the code duplication, but that's what was already done for 3.0 vs 3.3.2+ (i.e. if there is a change in a file, duplicate the file in sub-version-specific folders and remove it from scala-3), so I just continued the pattern. The changes are not extensive, and could be refactored out, but that should be done for 3.0 vs 3.3.2+ also if so.

I'm happy to take a look at that, but I'm not sure that should block 3.4 support given that it's already on the late side.

I can only plead, for this PR: I may have dug a hole, but it isn't a new hole; I'm just digging the existing one deeper.

[lihaoyi]

sgtm

[lihaoyi]

This is available as //github.com/com-lihaoyi/Ammonite/releases/download/3.0.0-M2/3.4-3.0.0-M2-9-88291dd8