fix PLT_VALIDATE_COMPILE interaction with 3-D code

Makes the "optimize.rktl" test suite pass when PLT_VALIDATE_COMPILE
is defined.
treat FFI primitives like other primitives internally

This change paves the way for JIT-inlining FFI operations
such as `ptr-ref`. Even without JIT treatment, the change
slightly reduces the overhead for calling FFI primitives.
racket/gui: small speed-ups in editor drawing path

Mostly, replace some method calls with field selectors (where the
path is important enough that it seems worthwhile).