prevent forged i18n marker injection & refresh namespace for i18n placeholders - #70363

fix(core): prevent forged i18n marker injection

Treat translated text as untrusted instead of allowing it to become compiler-generated i18n structure. Without validation, forged structural and binding markers can target declaration slots or expressions outside the source message and leave runtime metadata inconsistent with the DOM.

Reject reserved delimiters at the translation boundary and validate placeholder structure, node slots, and binding ranges before applying i18n opcodes. Preserve legitimate placeholder reordering, interpolations, and structural directive cases.

fix(core): refresh namespace for i18n placeholders

i18n predeclares TNode placeholders before element instructions select their final namespace. Promoting an SVG placeholder without refreshing this field leaves HTML metadata attached to an SVG DOM element, so SVG-specific binding validation can use the wrong security context.

Refresh the namespace from the current instruction state when adopting a placeholder and cover security-sensitive SMIL href animation bindings.

More context https://issuetracker.google.com/u/1/issues/550667019

What is the new behavior?

Translated literals can no longer contain Angular's reserved U+FFFD runtime marker.

loadTranslations({
  [messageId]: '�#0�Ready�/#0�',
});

The translation is rejected before rendering. Runtime validation also throws NG0700 if a structural marker targets an occupied declaration slot, preventing TNode corruption and the iframe[srcdoc] sanitization bypass.

Nowlements created from i18n placeholders now receive the namespace selected by their element instruction.

@Component({
  template: `
    <section i18n>
      Open profile
      <svg>
        <a>
          <set attributeName="href" [attr.to]="payload"></set>
        </a>
      </svg>
    </section>
  `,
})
class Profile{
   payload = 'javascript:alert("evil")';
}

Angular recognizes <set> as an SVG element, throws NG0910, and does not write the unsafe to attribute.