Migrate to promise based APIs after MV3 is landed

[melink14]

Except for event listeners most APIs that used callbacks before now support Promise return values. We should migrate to those.

In some cases, we've even created wrappers to transform the callback based code into promise based code.

rikaikun/extension/configuration.ts

Lines 40 to 48 in 8fd4bf4

	// Simply wrapper which makes `sync.get` `Promise` based.
	async function getStorage(): Promise<MutableConfig> {
	const config = await new Promise<MutableConfig>((resolve) => {
	chrome.storage.sync.get(defaultConfig, (cloudStorage) => {
	resolve(cloudStorage as MutableConfig);
	});
	});
	return config;
	}