Set up key backup using non-deprecated APIs

[andybalaam]

Depends on matrix-org/matrix-js-sdk#3935

Fixes element-hq/element-web#26323

Replace use of deprecated APIs to set up the key backup, meaning it works for the Rust crypto implementation as well as the legacy one.

This change:

• Adds a new Playwright test for creating, deleting, and re-creating a backup. This test reproduces the symptoms of the bug without the rest of this PR.
• Disables the Playwright test for legacy crypto, since it doesn't work quite the same there. The backup fails to delete, possibly because it has no keys inside it, or because we are deleting it too quickly after it was created. Since this bug only affects Rust crypto, I thought it would be OK only to run the test for Rust crypto.
• Adds a getClipboard method, and requests clipboard-read permission in the Playwright setup, so we can copy the security key to use later in the test.
• Adds a new optional argument, setupNewKeyBackup to accessSecretStorage so that we can pass in false in our case. We will set up the backup manually once we have access to the secret storage, so we don't want it set up automatically just because we are asking for access.
• Uses getCrypto to get hold of the crypto backend instead of the deprecated .crypto pattern.
• Uses resetKeyBackup to create a backup instead of the deprecated two-step prepareKeyBackupVersion + createKeyBackupVersion
• Expects scheduleAllGroupSessionsForBackup to be called inside resetKeyBackup because of Call scheduleAllGroupSessionsForBackup during resetKeyBackup matrix-js-sdk#3935
• Doesn't call deleteKeyBackupVersion any more when an unknown error is encountered. As per the comment in that section of the code, it is not clear what we should do in this situation, and we don't have the required information to perform the delete, so I've left it out.
• Fixes up the unit tests for CreateKeyBackupDialog to ensure we do call the code passed in to accessSecretStorage so that we can allow an error to leak out of them in the failure case.
• Wraps the error case unit test in a describe block so we can filter its error messages from the console without suppressing any legitimate errors from the other tests.
• Adds very basic unit tests for the previously-untested SecurityManager.accessSecretStorage

---

Here's what your changelog entry will look like:

🐛 Bug Fixes

• Set up key backup using non-deprecated APIs (#12005). Fixes Element-R: "Set up key backup" button doesn't work element-hq/element-web#26323. Contributed by @andybalaam.