[OW2] A few changes for Mei

[GreyFalcon-11737]

So if Mei is gonna be this underwhelming in OW2, can she at least get some minor changes?

Something like:

MEI

Button Configuration

• Checkbox to swap Alternate and Primary Fire, without impacting Icewall Deploy/Cancel buttons
• Default the button layout where Icicle is the Primary, and Frost is the Secondary.

Endothermic Blaster (Alternate Fire)

• Initial cast time reduced to 0.1 seconds, down from 0.4 seconds
• Cast time between shots reduced to 0.7 seconds, down from 0.8 seconds
• Ammo cost reduced to 5, down from 10.

Cryo-Freeze (Iceblock)

• Regains ammo at a rate of 30 per second.

Icewall

• Fix the bugs where Mei phases through the wall, or just in general doesn’t get raised up.