Feat: Allow CustomPhaseCommand to check if Solving Terminated Early

[Christopher-Chianelli]

Is your feature request related to a problem? Please describe.

A CustomPhaseCommand may take a long time to execute. As a result, there can be a long delay between when terminateEarly is called and when the Solver actually terminates since the Solver has to wait for the CustomPhaseCommand to finish.

Describe the solution you'd like

A method for a CustomPhaseCommand to check if solving was terminated so it can return early. These can include:

• Interrupting the Solver Thread
• Adding a new method to Score Director
• Adding a new method to Phase that is called by terminateEarly

Describe alternatives you've considered

See above.

Additional context

#1199