Add semantic analysis

[bgins]

Check.hs has the first steps needed for the check phase, but the majority of the work is yet to be completed. Semantic analysis should be implemented based on "Chapter 3: Validation" in the WebAssembly specification.

Validation will consist of two passes. The first pass collects type definitions at the module level, and the second pass validates the module. Check.hs has part of what is needed in the first pass. It collects type definitions, but it still needs to resolve InlineType and TypeUseWithDeclarations that appear on func components.

The Validation Algorithm in §7.3 should be studied before further work on this phase.