Switch to Rust crypto stack for all logins (matrix-org#12630)

* Use Rust crypto stack universally

Ignore the `feature_rust_crypto` and `RustCrypto.staged_rollout_percent`
settings, and just use RustCrypto everywhere.

* Remove labs setting for rust crypto

* Remove support for legacy crypto stack in `StorageManager`

We're not going to use the legacy stack any more.

* Update docs on `Features.RustCrypto`

* Remove now-unreachable `tryToUnlockSecretStorageWithDehydrationKey`

* Comment out test which doesn't work

* fix typo

playwright/e2e/crypto/crypto.spec.ts

@@ -438,7 +438,9 @@ test.describe("Cryptography", function () {
             if (cryptoBackend === "rust") {
                 await expect(lastE2eIcon).toHaveClass(/mx_EventTile_e2eIcon_warning/);
             } else {
-                await expect(lastE2eIcon).toHaveClass(/mx_EventTile_e2eIcon_normal/);
+                // skip this for now: the legacy option no longer actually gives us a legacy stack.
+                // We'll sort this out properly in https://github.com/matrix-org/matrix-react-sdk/pull/12662
+                // await expect(lastE2eIcon).toHaveClass(/mx_EventTile_e2eIcon_normal/);
             }
             await lastE2eIcon.focus();
             await expect(page.getByRole("tooltip")).toContainText("Encrypted by an unknown or deleted device.");