…ions

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

`bash` fix:
 - Add missing `:` separator in the path setter to avoid path corruption
 - Add missing quotes to avoid path interpretation

`zsh` fix:
 - Add missing `:` separator in the path setter to avoid path corruption
 - 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`](https://github.com/mamba-org/vscode-micromamba) which modify process environment and after login shell rc processing path entries end up in the end.

as generic env append/prepend can't handle path
separators, neither should it be handled here