This needs some render testing, but is destined to be part of master.
This also leads to a variety of other simplifications.
- IO are global symbols, so only need one list of linkage nodes (deferred)
- no longer need parse-context-wide 'inEntryPoint' state, entry-point is localized
- several parts of splitting/flattening are now localized
Rationalizes the entire tracking of the linker object nodes, effecting
GLSL, HLSL, and SPIR-V, to allow tracked objects to be fully edited before
their type snapshot for linker objects.
Should only effect things when the rest of the AST contained no reference to
the symbol, because normal AST nodes were not stale. Also will only effect such
objects when their types were edited.
