[web] Add identity client shared worker proxy

Summary:
[ENG-6767 : Introduce IdentityServiceClientWrapper proxy](https://linear.app/comm/issue/ENG-6767/introduce-identityserviceclientwrapper-proxy)

Adds IdentityServiceClientSharedProxy which proxies the identity service request to the shared worker. Each method gets a new worker request message and if it returns a value also a response message. IdentityServiceContextProvider can now optionally (behind a flag) return the proxy instead of the "real" identity client.

Depends on D11274

Test Plan:

• Make sure that if e.g. access token changes that the identity client on shared worker is recreated with new credentials
• generateNonce/getKeyserverKeys/uploadOneTimeKeys/publishWebPrekeys/getInboundKeysForUser/getOutboundKeysForUser/deleteUser/logInPasswordUser (everything except for the logInWalletUser) and made sure that they work

Reviewers: kamil, tomek

Reviewed By: kamil

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D11275