Build the applied and legacy directives from one resolved list

buildAppliedDirectives and buildDirectives each looked up the definition and walked the supplied and defaulted
arguments, and every call site called both. Now resolveDirectives does the lookup, the argument walk, the warnings and
the errors once, and appliedDirectives and legacyDirectives render the result. Call sites use withSdlDirectives.

The legacy list keeps its differences as named rules: no undeclared directives, only the first of a repeated
non-repeatable one (by the first declaration, like directivesOf), and descriptions only on defaulted arguments.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: oryan-block