fix(compiler-cli): `isCaseSensitive()` returns correct value (#36859)

Previously this method was returning the exact opposite value
than the correct one.
Also, calling `this.exists()` causes an infinite recursions,
so the actual file-system `fs.existsSync()` method is used
to ascertain the case-sensitivity of the file-system.

PR Close #36859

packages/compiler-cli/src/ngtsc/file_system/src/node_js_file_system.ts

@@ -68,7 +68,9 @@ export class NodeJSFileSystem implements FileSystem {
   }
   isCaseSensitive(): boolean {
     if (this._caseSensitive === undefined) {
-      this._caseSensitive = this.exists(togglePathCase(__filename));
+      // Note the use of the real file-system is intentional:
+      // `this.exists()` relies upon `isCaseSensitive()` so that would cause an infinite recursion.
+      this._caseSensitive = !fs.existsSync(togglePathCase(__filename));
     }
     return this._caseSensitive;
   }

packages/compiler-cli/src/ngtsc/file_system/test/node_js_file_system_spec.ts

@@ -153,14 +153,6 @@ describe('NodeJSFileSystem', () => {
       expect(mkdirCalls).toEqual([xPath, xyPath, xyzPath]);
     });
 
-    describe('removeDeep()', () => {
-      it('should delegate to fsExtra.remove()', () => {
-        const spy = spyOn(fsExtra, 'removeSync');
-        fs.removeDeep(abcPath);
-        expect(spy).toHaveBeenCalledWith(abcPath);
-      });
-    });
-
     it('should not fail if a directory (that did not exist before) does exist when trying to create it',
        () => {
          let abcPathExists = false;
@@ -228,4 +220,19 @@ describe('NodeJSFileSystem', () => {
       expect(isDirectorySpy).toHaveBeenCalledTimes(1);
     });
   });
+
+  describe('removeDeep()', () => {
+    it('should delegate to fsExtra.remove()', () => {
+      const spy = spyOn(fsExtra, 'removeSync');
+      fs.removeDeep(abcPath);
+      expect(spy).toHaveBeenCalledWith(abcPath);
+    });
+  });
+
+  describe('isCaseSensitive()', () => {
+    it('should return true if the FS is case-sensitive', () => {
+      const isCaseSensitive = !realFs.existsSync(__filename.toUpperCase());
+      expect(fs.isCaseSensitive()).toEqual(isCaseSensitive);
+    });
+  });
 });