fish completions: fix double-evaluation of commandline

[krobelus]

We capture the commandline tokens using fish's "commandline --tokenize" (-o). That function turns

echo 'some argument $(123)'

into two arguments while removing the quotes

echo
some argument $(123)

Later we pass "some argument $(123)" without quotes to the shell's "eval". This is wrong and causes spurious evaluation of the parenthesis as command substitution.

Fix this by escaping the arguments.

The downside of this change is that things like "$HOME" or "~" will no longer be escaped. Changing this requires changes in fish, which I'm working on.

Reproduce the issue by pasting the completion script at https://github.com/fish-shell/fish-shell/issues/10194#issuecomment-1879563545 to a file "grafana-manager.fish" and running inside fish

function grafana-manager; end
source grafana-manager.fish

Then type (without pressing Enter)

grafana-manager public-dashboards delete --organization-id 3 --dashboard-name "k8s (public)" <TAB>

Fixes https://github.com/fish-shell/fish-shell/issues/10194

[CLAassistant]

All committers have signed the CLA.

[stellarblaze]

@krobelus, do you know what needs to be done for this PR to be merged and included in the next release?

[stellarblaze]

• @marckhouzam, could you please take a look?

[krobelus]

The downside of this change is that things like "$HOME" or "~" will no longer be escaped.

The API to avoid this downside while still fixing the issue at hand has been merged in https://github.com/fish-shell/fish-shell/pull/10212, which will be in the upcoming fish release. It's fairly straightforward to upgrade to the new API, I can roll a patch by tomorrow.