LibJS: Disallow escape sequence/line continuation in use strict directive

https://tc39.es/ecma262/#sec-directive-prologues-and-the-use-strict-directive

A Use Strict Directive is an ExpressionStatement in a Directive Prologue
whose StringLiteral is either of the exact code point sequences
"use strict" or 'use strict'. A Use Strict Directive may not contain an
EscapeSequence or LineContinuation.

Libraries/LibJS/Tests/use-strict-directive.js

@@ -0,0 +1,48 @@
+test("valid 'use strict; directive", () => {
+    expect(
+        (() => {
+            "use strict";
+            return isStrictMode();
+        })()
+    ).toBeTrue();
+    expect(
+        (() => {
+            'use strict';
+            return isStrictMode();
+        })()
+    ).toBeTrue();
+});
+
+test("invalid 'use strict; directive", () => {
+    expect(
+        (() => {
+            " use strict ";
+            return isStrictMode();
+        })()
+    ).toBeFalse();
+    expect(
+        (() => {
+            `use strict`;
+            return isStrictMode();
+        })()
+    ).toBeFalse();
+    expect(
+        (() => {
+            "use\
+            strict";
+            return isStrictMode();
+        })()
+    ).toBeFalse();
+    expect(
+        (() => {
+            "use\ strict";
+            return isStrictMode();
+        })()
+    ).toBeFalse();
+    expect(
+        (() => {
+            "use \163trict";
+            return isStrictMode();
+        })()
+    ).toBeFalse();
+});