Update the official tutorial, "Groundwork" part

Discussed in https://github.com/HaxeFlixel/flixel/discussions/2521

^{Originally posted by NicklGames March 16, 2022}
Let me explain myself

If following the tutorial, when reaching this part

this will cause a bug, in which player will constantly move because it's telling to move the player every frame with no condition

It can be easily fixed tho, in 2 ways i know
1: Setting the speed to something only when player is moving and setting it to 0 when player is not

2: Adding a boolean that will tell if player is actually moving and move the player only if any of the keys is actually pressed

It really is easy, why not update the tutorial (if the reason that it IS easy, then why letting an intentional bug be in an OFFICIAL tutorial?)

Start with the official tutorial's "Groundwork" part and locate the movement section shown in the issue screenshots. Reproduce the tutorial to confirm the player moves without input, then update the tutorial so movement occurs only while input is active and verify the walkthrough no longer produces that behavior.