fix(bidi): handle uppercase values correctly (#14773)

The native `dir` attribute is case-insensitive, however our `dir` directive will normalize something like `RTL` to `ltr`. These changes account for different cases of the values.

src/cdk/bidi/dir.ts

@@ -47,9 +47,10 @@ export class Dir implements Directionality, AfterContentInit, OnDestroy {
   get dir(): Direction { return this._dir; }
   set dir(value: Direction) {
     const old = this._dir;
+    const normalizedValue = value ? value.toLowerCase() : value;
 
     this._rawDir = value;
-    this._dir = (value === 'ltr' || value === 'rtl') ? value : 'ltr';
+    this._dir = (normalizedValue === 'ltr' || normalizedValue === 'rtl') ? normalizedValue : 'ltr';
 
     if (old !== this._dir && this._isInitialized) {
       this.change.emit(this._dir);

src/cdk/bidi/directionality.spec.ts

@@ -11,7 +11,12 @@ describe('Directionality', () => {
 
     TestBed.configureTestingModule({
       imports: [BidiModule],
-      declarations: [ElementWithDir, ElementWithPredefinedAutoDir, InjectsDirectionality],
+      declarations: [
+        ElementWithDir,
+        ElementWithPredefinedAutoDir,
+        InjectsDirectionality,
+        ElementWithPredefinedUppercaseDir,
+      ],
       providers: [{provide: DIR_DOCUMENT, useFactory: () => fakeDocument}],
     }).compileComponents();
   }));
@@ -134,6 +139,13 @@ describe('Directionality', () => {
         expect(fixture.componentInstance.dir.value).toBe('ltr');
       });
 
+    it('should be case-insensitive', () => {
+      const fixture = TestBed.createComponent(ElementWithPredefinedUppercaseDir);
+      fixture.detectChanges();
+
+      expect(fixture.componentInstance.dir.value).toBe('rtl');
+    });
+
   });
 });
 
@@ -158,6 +170,14 @@ class ElementWithPredefinedAutoDir {
   @ViewChild(Dir) dir: Dir;
 }
 
+@Component({
+  template: '<div dir="RTL"></div>'
+})
+class ElementWithPredefinedUppercaseDir {
+  @ViewChild(Dir) dir: Dir;
+}
+
+
 /** Test component with Dir directive. */
 @Component({
   selector: 'injects-directionality',