in noImplicitReturns mode, also disallow "return;"

In --noImplicitReturns mode, if a function specifies a return type,
disallow empty "return;" statements.

Fixes #5916.

tests/baselines/reference/noImplicitReturnsWithoutReturnExpression.errors.txt

@@ -0,0 +1,34 @@
+tests/cases/compiler/noImplicitReturnsWithoutReturnExpression.ts(2,5): error TS7030: Not all code paths return a value.
+tests/cases/compiler/noImplicitReturnsWithoutReturnExpression.ts(22,9): error TS7030: Not all code paths return a value.
+
+
+==== tests/cases/compiler/noImplicitReturnsWithoutReturnExpression.ts (2 errors) ====
+    function isMissingReturnExpression(): number {
+        return;
+        ~~~~~~~
+!!! error TS7030: Not all code paths return a value.
+    }
+    
+    function isMissingReturnExpression2(): any {
+        return;
+    }
+    
+    function isMissingReturnExpression3(): number|void {
+        return;
+    }
+    
+    function isMissingReturnExpression4(): void {
+        return;
+    }
+    
+    function isMissingReturnExpression5(x) {
+        if (x) {
+            return 0;
+        }
+        else {
+            return;
+            ~~~~~~~
+!!! error TS7030: Not all code paths return a value.
+        }
+    }
+    

tests/baselines/reference/noImplicitReturnsWithoutReturnExpression.js

@@ -0,0 +1,48 @@
+//// [noImplicitReturnsWithoutReturnExpression.ts]
+function isMissingReturnExpression(): number {
+    return;
+}
+
+function isMissingReturnExpression2(): any {
+    return;
+}
+
+function isMissingReturnExpression3(): number|void {
+    return;
+}
+
+function isMissingReturnExpression4(): void {
+    return;
+}
+
+function isMissingReturnExpression5(x) {
+    if (x) {
+        return 0;
+    }
+    else {
+        return;
+    }
+}
+
+
+//// [noImplicitReturnsWithoutReturnExpression.js]
+function isMissingReturnExpression() {
+    return;
+}
+function isMissingReturnExpression2() {
+    return;
+}
+function isMissingReturnExpression3() {
+    return;
+}
+function isMissingReturnExpression4() {
+    return;
+}
+function isMissingReturnExpression5(x) {
+    if (x) {
+        return 0;
+    }
+    else {
+        return;
+    }
+}

tests/cases/compiler/noImplicitReturnsWithoutReturnExpression.ts

@@ -0,0 +1,25 @@
+// @noImplicitReturns: true
+function isMissingReturnExpression(): number {
+    return;
+}
+
+function isMissingReturnExpression2(): any {
+    return;
+}
+
+function isMissingReturnExpression3(): number|void {
+    return;
+}
+
+function isMissingReturnExpression4(): void {
+    return;
+}
+
+function isMissingReturnExpression5(x) {
+    if (x) {
+        return 0;
+    }
+    else {
+        return;
+    }
+}