Add regression tests

Author: slavapestov

validation-test/compiler_crashers_fixed/issue-52841.swift

@@ -0,0 +1,11 @@
+// RUN: %target-swift-frontend -emit-ir -g %s
+
+protocol Foo {
+  associatedtype ErrorType: Error
+}
+
+extension Array: Error where Element: Error {}
+
+class Bar<A: Foo> {
+  func doSomething(with result: Result<Any, [A.ErrorType]>) {}
+}

validation-test/compiler_crashers_fixed/issue-66572.swift

@@ -0,0 +1,12 @@
+// RUN: %target-swift-frontend -emit-ir %s
+
+public final class TypedNode {
+    public var property: String?
+    
+    public func withProperty(_ generator: (Self) -> String) -> Self {
+        self.property = generator(self)
+        return self
+    }
+}
+
+let tree = TypedNode().withProperty { "\($0)" }

validation-test/compiler_crashers_fixed/issue-66590.swift

@@ -0,0 +1,6 @@
+// RUN: not %target-swift-frontend -typecheck %s
+
+struct A<X> {}
+extension A<A<Int>.B> {
+  struct B {}
+}