Support variables in editor path

### Godot version

4.4.1

### VS Code version

1.103.1

### Godot Tools VS Code extension version

2.5.1

### System information

Windows 10, Ubuntu, Fedora

### Problem statement

Godot project contains the relevant version of Godot engine, this is then loaded using either a Linux or windows script which provides environment variables which filter through to VSCode. Since we have people on Linux and people on Windows, we can't use an absolute path for the editor.

### Proposed solution

Variables would allow the user to use something like `${env:GODOT}` to provide the editor location which would resolve the issues with Linux vs Windows.