Fix pinch gestures for web

[ghost]

Adds previousPositionA and previousPositionB to the rgestures.h's Touch struct to keep track of the previous Pinch positions. Didn't want to try to reuse downPositionA and downPositionB for this case to not break the other gestures that use them and are working properly.

Assign the values of previousPositionA and previousPositionB during the event.touchAction == TOUCH_ACTION_DOWN instead, so they can exist before the event.touchAction == TOUCH_ACTION_MOVE.

Removes the now no longer used GESTURES.Touch.downPositionA and GESTURES.Touch.downPositionB assigns inside the event.touchAction == TOUCH_ACTION_MOVE.

Changes the MINIMUM_PINCH check to now use the previousPositionA and previousPositionB.

Changes the criteria to define if it's GESTURE_PINCH_IN or GESTURE_PINCH_OUT by checking the distance between previousPosition and moveDownPosition. If previousPosition distance is larger than moveDownPosition distance, then it's a GESTURE_PINCH_IN, else it's a GESTURE_PINCH_OUT.

Fixes #1963.

[SAOMDVN]

Worked on Safari on iOS 16!

[raysan5]

@ubkp thanks for the review! great improvement! :)