refactor(core): move sanitization into core (#22540)

This is in preparation of having Ivy have sanitization inline.

PR Close #22540

packages/core/src/sanitization/security.ts

@@ -0,0 +1,34 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+/**
+ * A SecurityContext marks a location that has dangerous security implications, e.g. a DOM property
+ * like `innerHTML` that could cause Cross Site Scripting (XSS) security bugs when improperly
+ * handled.
+ *
+ * See DomSanitizer for more details on security in Angular applications.
+ *
+ * @stable
+ */
+export enum SecurityContext {
+  NONE = 0,
+  HTML = 1,
+  STYLE = 2,
+  SCRIPT = 3,
+  URL = 4,
+  RESOURCE_URL = 5,
+}
+
+/**
+ * Sanitizer is used by the views to sanitize potentially dangerous values.
+ *
+ * @stable
+ */
+export abstract class Sanitizer {
+  abstract sanitize(context: SecurityContext, value: {}|string|null): string|null;
+}