Fix App Check typings

[hsubox76]

Fixes #5569

The two public facing providers (Custom and RecaptchaV3) implement an internal interface AppCheckProvider but they hide some of their public methods, causing them to be inconsistent with the internal interface.

If I tag AppCheckProvider @internal, the "implements AppCheckProvider" is still there on the two public types and there's an error because it can't find it.

I don't want to get rid of the "implements" because it is a helpful check in the internal code.

[changeset-bot]

⚠️ No Changeset found

Latest commit: ccc0c36

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[google-oss-bot]

Binary Size Report

Affected SDKs

No changes between base commit (e70de62) and head commit (a937017).

Test Logs

• Base (e70de620): https://github.com/firebase/firebase-js-sdk/actions/runs/1296121523
• Head (a9370178): https://github.com/firebase/firebase-js-sdk/actions/runs/1296259720

[google-oss-bot]

Size Analysis Report

Affected Products

No changes between base commit (e70de62) and head commit (a937017).

Test Logs

• Base (e70de62): https://github.com/firebase/firebase-js-sdk/actions/runs/1296121523
• Head (a937017): https://github.com/firebase/firebase-js-sdk/actions/runs/1296259720

[Feiyang1]

@hsubox76 please add a changeset