D bindings: fix mangling error, use improved BindBC-Common API (bkara…

…dzic#3201)

* Reformatted comments; fixed a couple of oversights

* D bindings: deterministic sub-struct order

* Added missing default to IDL

* Fixed sub-struct linkage; regenerate D binds

* Culled D bindings for header-only C++ functions

* Added missing default to bgfx.idl

* cppinline now supported by all auto-gen bindings

The pattern "func.cppinline and not func.conly" is to make sure that C bindings for `bgfx_vertex_layout_has` are still generated.

* Fix mangling issue; use updated BindBC-Common API