Blentran: implement linedef actions for all blendmode strengths
The new blending mode features for midtextures and FOFs from !1534 (closed) are excellent, but only allow additive/subtractive/reverse subtractive midtextures at 100% strength. Instead of only using actions 910 to 913 for additive, subtractive, reverse subtractive and modulate respectively, this branch changes it to the following:
- 910 to 919 are used for 100% additive to 10% additive.
- 920 to 929 are used for 100% subtractive to 10% subtractive.
- 930 to 939 are used for 100% reverse subtractive to 10% reverse subtractive.
- 940 is used for modulate.