Add Gif Snapshot Handler

[stevePanella]

The gif() function in paparazzi creates multiple images per test. The resulting files each have an appended index, for example:

• myGifTest0.png
• myGifTest1.png
• myGifTest2.png
  etc...

When validating against existing snapshots, Paparazzi currently looks for the file name without the appended index, since this is what non-gif snapshots need to validate against. For example:

• mySnapshotTest.png

To solve this problem, this PR creates a GifSnapshotHandler which will ensure that the correct index is appended to each file name before validating against the golden images. We can easily hook this up into gif tests by overriding the snapshotHandler in our test rule

@get: Rule
    val paparazzi = Paparazzi(
        ...
        snapshotHandler = determineGifHandler(),
    )
    

[imayank91]

Where are you using this method?

[stevePanella]

this will be used to override the regular snapshot handler when we actually go to use this in our test rule. Like this:

@get: Rule
    val paparazzi = Paparazzi(
        ...
        snapshotHandler = determineGifHandler(),
    )