[RyuJit Wasm] Crossgen Wasm Namespace Refactor

We should ensure that new Wasm functionality for crossgen is added to the appropriate namespaces. I.e., if we need to add Wasm-specific logic in several places in `ILCompiler.DependencyAnalysis`, we should potentially just move Wasm-specific functionality into that root namespace for clarity to avoid unneeded namespace nesting and `using`s.