[validation] Update entry points validation v-0020

Remove irrelevant unit tests
Add/Update ValdiateEntryPoints function
Update known failure file

Bug: tint:296
Change-Id: I7d5c9c96fcca29f3e0a4c0315eb8ce869160a3ea
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/32220
Reviewed-by: David Neto <dneto@google.com>
Commit-Queue: David Neto <dneto@google.com>

src/validator/validator_impl.h

@@ -113,6 +113,10 @@ class ValidatorImpl {
   /// @param c the case statement to check
   /// @returns true if the valdiation was successful
   bool ValidateCase(const ast::CaseStatement* c);
+  /// Validates entry points
+  /// @param funcs the functions to check
+  /// @returns true if the valdiation was successful
+  bool ValidateEntryPoint(const ast::FunctionList& funcs);
 
  private:
   std::string error_;