Create documentation and strong types, similar to signify-browser-extension

[2byrds]

@lenkan and others will use polaris-web without knowledge of the signify-browser-extension and currently that's where the interface and methods are documented.
Improve this repo to 'stand-alone' with documentation that guides and extension implementor to be to quickly understand the inputs/outputs.
Also consider a future issue to address versioning as we move forward (potentially create additional issues).

[lenkan]

One additional thing that would be good to include is the error handling. How does the content script indicate to polaris-web that a particular request has failed?

[2byrds]

One additional thing that would be good to include is the error handling. How does the content script indicate to polaris-web that a particular request has failed?

@HunnySajid per @lenkan question can you respond here and let us know if this can be closed?

[lenkan]

Regarding the error handling. There is now a mechanism for that, see for example this test here:

polaris-web/src/client.test.ts

Lines 145 to 158 in bcb5283

	test("Should throw when responding with error", async () => {
	const client = createClient();
	const extension = createMockExtension();
	handleMessage.mockImplementationOnce((ev) => {
	extension.reject(ev, new Error("Declined"));
	});
	await expect(() =>
	client.signData({
	items: [randomBytes(10).toString("hex")],
	}),
	).rejects.toThrow("Declined");
	});

and the reject "mock" implementation:

polaris-web/src/client.test.ts

Lines 21 to 27 in bcb5283

	function reject(ev: MessageEvent, reason?: Error) {
	postMessage({
	type,
	requestId: ev.data.requestId,
	error: reason?.message ?? "Something went wrong",
	});
	}

In other words, if you add a "error" property to the response message, it will be treated as an error.

[lenkan]

Also, the example app provides sufficient standalone documentation in my opinion.