Support for running build command from a task

[SanjoSolutions]

This adds support for running the build command as a task. This has a use case for a build pipeline with multiple steps (i.e. also compiling Python scripts to a ts4scripts file).

tasks.json:

{
  // See https://go.microsoft.com/fwlink/?LinkId=733558
  // for the documentation about the tasks.json format
  "version": "2.0.0",
  "tasks": [
    {
      "label": "build package",
      "command": "${command:s4tk.workspace.build}"
    },
    {
      "label": "build scripts",
      "type": "shell",
      "command": "python ../sims4-mod-development-tools/compile.py"
    },
    {
      "label": "build",
      "dependsOn": ["build package", "build scripts"],
      "problemMatcher": [],
      "group": {
        "kind": "build",
        "isDefault": true
      }
    },
    {
      "label": "deploy",
      "type": "shell",
      "command": "./deploy.sh"
    },
    {
      "label": "build and deploy",
      "dependsOrder": "sequence",
      "dependsOn": ["build", "deploy"]
    }
  ]
}

Before the changes of this PR, it seems that when the command was run as a task like the task "build package" from the tasks.json above, the extension received some JSON object as first argument which was not a URI. With the added URI check from this PR, the command works in both cases, running from command palette or via a task.