Avoid taking regular canvas snapshots with replay if canvas does not change

[mydea]

Currently, we take a canvas snapshot every 2 seconds. However, if we knew that the canvas hasn't changed at all, we could skip this.

[billyvg]

As a note, rrweb currently checks if a snapshot is different than the previous one before sending (so saving on network transfer), but does not check if canvas is "dirty" before snapshotting, which would be a big win perf wise to avoid the snapshot in the first place.

[billyvg]

I believe the only way to do this is to wrap the canvas context draw methods to track when/if the canvas has been changed. Canvas replays are not a big focus for us right now, so we're going to close this ticket. This optimization can be a bit risky and not something we want to take on right now.