Avoid infinite loop checking yield expression (#21728)

* Avoid infinite loop checking yield expression

* Revert now-unneeded change

* Revert test filename changes

Author: Andy

tests/baselines/reference/yieldExpressionInFlowLoop.js

@@ -0,0 +1,16 @@
+//// [yieldExpressionInFlowLoop.ts]
+function* f() {
+    let result;
+    while (1) {
+        result = yield result;
+    }
+}
+
+
+//// [yieldExpressionInFlowLoop.js]
+function* f() {
+    let result;
+    while (1) {
+        result = yield result;
+    }
+}

tests/baselines/reference/yieldExpressionInFlowLoop.symbols

@@ -0,0 +1,14 @@
+=== tests/cases/compiler/yieldExpressionInFlowLoop.ts ===
+function* f() {
+>f : Symbol(f, Decl(yieldExpressionInFlowLoop.ts, 0, 0))
+
+    let result;
+>result : Symbol(result, Decl(yieldExpressionInFlowLoop.ts, 1, 7))
+
+    while (1) {
+        result = yield result;
+>result : Symbol(result, Decl(yieldExpressionInFlowLoop.ts, 1, 7))
+>result : Symbol(result, Decl(yieldExpressionInFlowLoop.ts, 1, 7))
+    }
+}
+

tests/baselines/reference/yieldExpressionInFlowLoop.types

@@ -0,0 +1,18 @@
+=== tests/cases/compiler/yieldExpressionInFlowLoop.ts ===
+function* f() {
+>f : () => IterableIterator<any>
+
+    let result;
+>result : any
+
+    while (1) {
+>1 : 1
+
+        result = yield result;
+>result = yield result : any
+>result : any
+>yield result : any
+>result : any
+    }
+}
+

tests/cases/compiler/yieldExpressionInFlowLoop.ts

@@ -0,0 +1,9 @@
+// @noImplicitAny: true
+// @target: es6
+
+function* f() {
+    let result;
+    while (1) {
+        result = yield result;
+    }
+}