Add a "slow" type checker performance test for rdar://problem/46713933

Author: DougGregor

validation-test/Sema/type_checker_perf/slow/rdar46713933.swift

@@ -0,0 +1,13 @@
+// RUN: %target-typecheck-verify-swift
+
+func wrap<T>(_ key: String, _ value: T) -> T { return value }
+func wrap<T: ExpressibleByIntegerLiteral>(_ key: String, _ value: T) -> T { return value }
+func wrap<T: ExpressibleByFloatLiteral>(_ key: String, _ value: T) -> T { return value }
+func wrap<T: ExpressibleByStringLiteral>(_ key: String, _ value: T) -> T { return value }
+
+func wrapped(i: Int) -> Int {
+  // FIXME: When this stops being "too complex", turn the integer value into
+  // an integer literal.
+  // expected-error@+1{{reasonable time}}
+  return wrap("1", i) + wrap("1", i) + wrap("1", i) + wrap("1", i)
+}