debugger beta: Fix spawning debug tasks with Fish shell

[Anthony-Eid]

This fixes the issue that caused #31743 to revert this commit aab7620

The Fish shell doesn't accept empty strings as arguments. This causes problems when running locators that potentially have empty arguments, like the cargo locator. Thus, it makes it impossible for Zed to properly spawn a debug task based on a locator, which mostly affects debug configs created by a runnable icon.

We now remove task args that are empty after resolving their environmental variables.

Release Notes:

• N/A

[WeetHet]

I think the better approach would be to do what I and other people already proposed earlier and use /bin/sh for runnables by default so we don't have to adjust our code for all shells

[Anthony-Eid]

@WeetHet This PR has been sale since I've been thinking about going with my approach or your idea for a bit. I also got better with the debugger launch too.

I'm leaning towards the /bin/sh idea and defaulting to powershell on windows. I'm just worried if a user has a custom theme or something that affects the output of a command it won't show up if we default to bash/zsh/powershell

[WeetHet]

I'm leaning towards the /bin/sh idea and defaulting to powershell on windows. I'm just worried if a user has a custom theme or something that affects the output of a command it won't show up if we default to bash/zsh/powershell

We can add an ability to choose a shell (withou any guarantees than nothing would break), but realistically, user's theme should be the least of our worries and we already acquire the environment properly so nothing else should change

[Anthony-Eid]

@WeetHet I talked with the team and we're going with the /bin/sh solution and defaulting to powershell on windows. I'll push a fix for this later today.