[Macros] Update the name and argument list for the @Task function body macro.

[hborla]

• Use @Task for the macro name, because it always expands to a call to Task.init.
• Add a parameter for specifying a global actor. Applying @Task with no global actor parameter will infer the isolation of the context on the closure. If a global actor is specified, the macro will use it as a global actor attribute on the closure.
• Add parameters for name and priority, which are copied over to the Task.init call.

For example:

func perform() async { ... }

func acceptClosure(_ closure: @escaping () -> Void) { ... }

func test() {
  acceptClosure { @Task(name: "MyTask") in
    await perform()
  }
}

The macro expands to

func test() {
  acceptClosure {
    Task(name: "MyTask") {
      await perform()
    }
  }
}

[hborla]

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[hborla]

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[hborla]

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[hborla]

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