Check symbol kind before indexing constant qualifiers

[mindaugasrukas]

Check isClassOrModule() before indexing a constant as a class/module qualifier. This replaces the cast in the condition with a symbol-kind check.

Motivation

A constant assigned from a method call can be represented as a field symbol. Indexing an include that references it currently calls asClassOrModuleRef() before checking the symbol kind, triggering the kind() == Kind::ClassOrModule assertion.

The included regression reproduces this with:

module Helpers
  Dynamic = build_helpers

  class Client
    include Dynamic
  end
end

The kind check lets indexing continue while preserving the ordinary constant reference. The regression also covers a statically declared module referenced through Helpers::Static.

Test plan

• Confirmed the regression triggers the class/module assertion before the fix.
• Added a snapshot test covering dynamic constants and static module qualifiers.
• Ran ./bazel test --config=dev --jobs=6 //test/scip with this patch alone: all 60 tests passed.
• Built //main:scip-ruby with --config=dev and verified the dynamic-include reproduction produces an index accepted by the SCIP decoder.

Validation ran on macOS ARM64 using the macOS 14.4 SDK with the repository's LLVM 15 toolchain; the SDK selection was local to the validation checkout and is not part of this patch.