Use URL-based path resolution in HTTPStore

[manzt]

In #42 we migrated from URL-based path resolution to a more simple string concatenation. This PR fixes the same issue as #42 but reverts back to using URL.

It also adds a feature requested for forwarding search query params when resolving the new URL, so that an HTTPStore can be instantiated as follows:

const store = new HTTPStore("https://example.com/data.zarr?hello=world");
store.getItem('.zarray') // requests "https://example.com/data.zarr/.zarray?hello=world"

Generally I'd be in favor of migrating the type of HTTPStore.url to URL, but since it is a public field I have set it to a generic (with default to string).

cc: @ilan-gold