Add support for browser extensions

[clangenb]

Current state:

• Enconter-js: should have the support to use the injector now with a similar interface to polkadot-js/api's tx interface.

Currently blocked:

• needs Add support for trusted getter/calls that have been signed with an extension-dapp signer worker#1610 because of wrong signRaw signature for polkadotjs due to u8aWrapBytes that forced adding <Bytes>...<Bytes> to payload before "sign" function polkadot-js/extension#1357

[brenzi]

I was able to run this e2e on the public paseo sidechain after upgrade to 0.14.1

observations:

1. BUG: shielding: asks me twice to sign the same extrinsic. But the first extrinsic works as expected
2. send privately: 2 signing interactions: nonce + transfer
3. unshield: 2 signing interactions: nonce + unshield