A followup to #171066 fixing zsh and fish shells implementations

[anton-matosov]

#171066 introduced a fix for applying PATH prefix on macOS login shells that resolved #99878. However it had little issues for each shell implementation.
This PR contains the following fixes:

bash fix:

• Add missing quotes to avoid path interpretation

zsh fix:

• Add missing quotes to avoid path interpretation
• Move patching outside of .zprofile check as clean macOS install doesn't include this file, nevertheless PATH patching should still happen

fish fix:

• use set -gx PATH instead of fish_add_path as the latter has no effect on updating the path if entries already exist in it. Which is the case for some extensions, like vscode-micromamba which modify process environment and after login shell rc processing path entries end up in the end.

[anton-matosov]

I just found that there a second implementation of variables application #179476 that uses {applyAtShellIntegration: true} option and it works for all types of modification and works better in fish as it runs after fish.config and conf.d configs.
(Before I found it I extended original PATH only fix to work with all mutator types to patch up macOS behavior https://github.com/microsoft/vscode/compare/main...anton-matosov:vscode:implement-all-environment-mutations-for-shell-integrations?expand=1)

Considering that #179476 provides a complete implementation that works for all mutation types and for all shells, including login shell on mac. Shall the workaround for PATH (via VSCODE_PATH_PREFIX) be removed?
Moreover, if both VSCODE_PATH_PREFIX and {applyAtShellIntegration: true} are used, PATH ends up prepended twice on mac.

--
Note
I've tested on mac with append/prepend/replace for PATH for all shells, and it works, but still has a bug of missing : that glues paths on append/prepend. PR with fixes #223450

[Tyriar]

Thanks for the fix and investigation! Looks reasonable and fairly safe to me.

Also yes for #223450 the path separator must be provided by the extension

[Tyriar]

FYI @meganrogge in case you notice anything going wrong with zsh which has the biggest change.