Add tests for GRS transform cancellation

[rahat2134]

Fix part of #2465

This PR adds tests to verify that cancellation works properly for the GRS (Grab, Rotate, Scale) transformation operations.

I implemented tests that:
Create a rectangle
Start a transform operation (G/R/S)
Move the cursor to change the transform
Cancel the operation
Verify the transform is unchanged after cancellation

[0HyperCube]

Thanks for the contribution; the code and approach look good.

Please can you also add a testcase that doesn't cancel to ensure that we don't get the original transform in that case? This ensures that we are actually testing that the cancelling works.

[rahat2134]

@0HyperCube @Keavon PTAL!

[0HyperCube]

Look good; thanks for the contribution.