Expose P_LineIsBlocking to Lua

Technically PTR_LineIsBlocking, but I renamed it for consistency's sake, not just in Lua. Simply tells you whether or not an object would be blocked by a line if said object attempted to cross it.

Test exe and mod:

lineisblockingtest.exe

L_LineIsBlockingTest.lua

added 193 commits

• a977fd60...a68440c4 - 192 commits from branch STJr:next
• 774cce8f - Merge branch SRB2:next into blockedexposed

Compare with previous version

added 347 commits

• 774cce8f...106a98ce - 346 commits from branch STJr:next
• c159987a - Merge branch SRB2:next into blockedexposed

Compare with previous version

merged

mentioned in commit 4edebbe6