Add "allowflip" Parameter to P_DoJump

Basically !2088 (closed) but good. Adds a boolean parameter to `P_DoJump` that controls whether the function should flip you in a jump flip sector. Set to false for bounces and while in quicksand. Set to true for all other proper jumps.

added 140 commits

• ecf950e7...a68440c4 - 139 commits from branch STJr:next
• e5d16e71 - Merge branch SRB2:next into setflip

Compare with previous version

added 97 commits

• e5d16e71...5fc7a5c2 - 96 commits from branch STJr:next
• c2c15760 - Merge branch 'next' into 'setflip'

Compare with previous version

added 223 commits

• c2c15760...8c1cd738 - 222 commits from branch STJr:next
• e6802774 - Merge branch 'next' into 'setflip'

Compare with previous version

added 29 commits

• e6802774...106a98ce - 28 commits from branch STJr:next
• 530c93c1 - Merge branch SRB2:next into setflip

Compare with previous version

merged

mentioned in commit 474d112a

mentioned in merge request !2332 (closed)