MAINT-3699 new shaders supporting alpha blend/mask rigged content.

indra/llprimitive/lltextureentry.h

indra/llrender/llglslshader.cpp

indra/llrender/llshadermgr.cpp

...s/shaders/class1/deferred/attachmentAlphaMaskShadowF.glsl

...tings/shaders/class1/deferred/attachmentAlphaShadowF.glsl

...tings/shaders/class1/deferred/attachmentAlphaShadowV.glsl

...tings/shaders/class1/deferred/avatarAlphaMaskShadowF.glsl

..._settings/shaders/class1/deferred/avatarAlphaShadowF.glsl

..._settings/shaders/class1/deferred/avatarAlphaShadowV.glsl

indra/newview/lldrawpoolavatar.cpp

indra/newview/lldrawpoolavatar.h

indra/newview/llviewershadermgr.cpp

indra/newview/llviewershadermgr.h