Move default JSA path to $HOME/.cache - #9692

See #9667 which this is intended to fix.

I'm going to hold off on the default location change for now and merge the config for both 10.0 and 10.1.

I like the new default but it's a pretty visible change that should probably bake in jruby-head for a while (and I don't think it should be backported to 10.0).

This now contains just the default location change (to $HOME/.cache), with the configurable JSA home merged from #9698. Will merge after 10.1.2.0 and let it bake in jruby-head for a bit.

I wonder if it's best to assume $HOME/.cache exists here. Other platforms like Mac have a different path for such data, and depending on the host, the operator might have defined it otherwise using the XDG_CACHE_HOME environment variable.

Well, that is a fair point, but is it worse than assuming the JRuby install location is writable? I'm trying to find a better option that allows users to get the benefit of the JSA file without requiring that.

Presumably this is also why the Debian package defaults to .cache. I want to reduce the amount of third-party patching required to maintain JRuby packages.

FWIW on my MacOS machine I do have a .cache directory, containing several Ruby-related items and a few from packages I've installed with Homebrew:

$ ls -1 ~/.cache                    
bashbrew
codex-runtimes
gem
install4j
javasharedresources
jruby
opencode
rbs
rubocop_cache
ruby-install
uv
vllm

Interestingly, the javasharedresources directory is put there by IBM's OpenJ9 JVM (Semeru) as a place to store that JVM's equivalent of AppCDS JSA files:

eclipse-openj9/openj9#2862