Execute typechecks eagerly when within a constraint (#964)

This changes the language to check all types eagerly when within a type constraint.

This addresses two regressions in the language:

1. Type constraints are too relaxed (listing/mapping parameters may not be checked)
2. Failing type constraints hide members that were forced during execution of the constraint

pkl-core/src/test/files/LanguageSnippetTests/input-helper/classes/MyClass.pkl

@@ -0,0 +1,9 @@
+typealias EmailAddress = String(matches(Regex(#".+@\S+|.+<\S+@\S+>"#)))
+
+class MyClass {
+  emails: Listing<EmailAddress>
+}
+
+myClass: MyClass
+
+others: Listing<module(this != module)>

pkl-core/src/test/files/LanguageSnippetTests/input-helper/classes/myClass1.pkl

@@ -0,0 +1,7 @@
+amends ".../input-helper/classes/MyClass.pkl"
+
+myClass {
+  emails {
+    "baz@bar.com"
+  }
+}