More user-friendly search weighing in `#`/`@` autocompletion

### Your use case

#### What would you like to do?

Change the algorithm that searches for rooms and users to be something like this;
- Try to match input against display names
- Try to match input against localparts
- Try to match input against serverparts

#### Why would you like to do it?

When wanting to mention a room, it's annoying when the room name is the same as a server name.

For instance, if i would like to mention a room with the word "matrix" in it, I first get dozens of matches from the `matrix.org` server, as "matrix" is in the `matrix.org` serverpart.

Thus, i think first weighing on displaynames, then on localparts, then on serverparts, could give a more subtle "good feel" about mentioning different users and rooms, "it just works".

(Thus, this is also a design question)

### Have you considered any alternatives?

_No response_

### Additional context

Related to #19096 (#18757), ranking same-space rooms above not-same-space rooms could help other UX problems, this is related to it because it also deals with finding rooms in a "weighing" manner.