Improve `matrix-search` behavior, attribute APIs, docs: - `apisearch` will allow calling /search on the homeserver (via `mwc.api.search(matrixSpecSearchBody)`, like before) - `quicksearch` will load the joined rooms as HTML datalist to the input (be can be used in conjunction or independent` - `quicksearch-events` will load the events from attribute as JSON stringyfied Array of MatrixEvent(s) - Fix the bug of datalist ID being "not unique" in the DOM (therefore also not in JS window/document, and being shared across instances of matrix-search; not what we wanted) - add `legend` and `placeholder` attributes for customizing what is shown on the screen