Recognize CODE definitions

[tulushev]

Teach forth-lsp to recognize CODE name ... END-CODE definitions.

This fixes false undefined-word diagnostics for words defined with CODE, for example VFX Forth code like:

CODE syscall0    \ nr -- r
  MOV  RAX, RBX
  SYSCALL
  MOV  RBX, RAX
  NEXT,
END-CODE

: sys-gettid ( -- tid )
  SYS_gettid syscall0
;

Before this change, syscall0 was not indexed as a definition, so later uses were reported as Undefined word.