Runnables don't work for folder-local tool installations

[WeetHet]

Check for existing issues

• Completed

Describe the bug / provide steps to reproduce it

Recently, my PR to enable using rust-analyzer from PATH was merged. After that I've decided to use a nix + direnv based installation which does not expose cargo or any other rust binary to the PATH. This is problematic, because if I understand correctly, currently runnables don't use delegate.which to determine the PATH to the binaries, instead just using the name. It doesn't work with directory local installations as right now create_terminal function from project/terminals.rs does not pass the full environment (the one acquired by executing delegate.shell_env) to the executed task.

The two possible solutions might be

1. Use delegate.which for runnables, falling back to just the name
2. Pass the shell_env to all task which is, in my opinion better, as it allows in the future to just use sh or something similar for language defined runnables without needing to worry about not having adequate environment variables set, therefore allowing for more advanced predefined tasks
   See the create_terminal function to understand what environment we are using right now

Environment

Zed: v0.140.4 (Zed Preview)
OS: macOS 14.5.0
Memory: 8 GiB
Architecture: aarch64

[WeetHet]

Also, in my opinion, some of the instances of Command should be using which as well, at least the language related ones 100% should do that