script: Initial stubs for Credential Management API (#38839)

Stubs `Credential`, `CredentialContainer`, and `PasswordCredential` and
adds the credentials attribute to navigator.

Testing: WPT
Fixes: Partially #38788

---------

Signed-off-by: Ashwin Naren <arihant2math@gmail.com>

components/script/dom/credentialmanagement/credential.rs

@@ -0,0 +1,73 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+use std::rc::Rc;
+
+use dom_struct::dom_struct;
+use script_bindings::realms::{AlreadyInRealm, InRealm};
+use script_bindings::str::{DOMString, USVString};
+
+use crate::dom::bindings::codegen::Bindings::CredentialBinding::CredentialMethods;
+use crate::dom::bindings::codegen::DomTypeHolder::DomTypeHolder;
+use crate::dom::bindings::reflector::{Reflector, reflect_dom_object};
+use crate::dom::bindings::root::DomRoot;
+use crate::dom::globalscope::GlobalScope;
+use crate::dom::promise::Promise;
+use crate::dom::window::Window;
+use crate::script_runtime::CanGc;
+
+#[dom_struct]
+pub(crate) struct Credential {
+    reflector_: Reflector,
+    id: USVString,
+    credential_type: DOMString,
+}
+
+impl Credential {
+    pub(crate) fn new_inherited(id: USVString, credential_type: DOMString) -> Credential {
+        Credential {
+            reflector_: Reflector::new(),
+            id,
+            credential_type,
+        }
+    }
+
+    #[expect(dead_code)]
+    pub(crate) fn new(
+        global: &GlobalScope,
+        id: USVString,
+        credential_type: DOMString,
+        can_gc: CanGc,
+    ) -> DomRoot<Credential> {
+        reflect_dom_object(
+            Box::new(Credential::new_inherited(id, credential_type)),
+            global,
+            can_gc,
+        )
+    }
+}
+
+impl CredentialMethods<DomTypeHolder> for Credential {
+    // https://www.w3.org/TR/credential-management-1/#dom-credential-id
+    fn Id(&self) -> USVString {
+        self.id.clone()
+    }
+
+    // https://www.w3.org/TR/credential-management-1/#dom-credential-type
+    fn Type(&self) -> DOMString {
+        self.credential_type.clone()
+    }
+
+    // https://www.w3.org/TR/credential-management-1/#dom-credential-isconditionalmediationavailable
+    fn IsConditionalMediationAvailable(_global: &Window) -> Rc<Promise> {
+        let in_realm_proof = AlreadyInRealm::assert::<DomTypeHolder>();
+        // FIXME:(arihant2math) return false
+        Promise::new_in_current_realm(InRealm::Already(&in_realm_proof), CanGc::note())
+    }
+
+    // https://www.w3.org/TR/credential-management-1/#dom-credential-willrequestconditionalcreation
+    fn WillRequestConditionalCreation(_global: &Window) -> Rc<Promise> {
+        let in_realm_proof = AlreadyInRealm::assert::<DomTypeHolder>();
+        Promise::new_in_current_realm(InRealm::Already(&in_realm_proof), CanGc::note())
+    }
+}