ACTUALLY implement a Bustable Floor Player Flag since !1163 removed the one that it used to have

!1163 (merged), despite what its name and description may suggest, actually does not contain a Bustable Floor Player Flag. PF_CANBUSTFLOORS was completely axed in the last commit made for the merge, and as such never made it into next.

This merge request fixes that, reimplementing PF_CANBUSTFLOORS using new code that works with P_CheckBustableBlocks instead of having dedicated checks. Note that none of the original code was used, this was made completely from scratch.

Anyways, here's a lua that tests this merge request. PF_CANBUSTFLOORS will be applied for as long as you hold down the Custom 1 button.