[Feature] Add basic functionality to the mention_input_bar component

[ZhangHanDong]

Add basic functionality to the mention_input_bar component. For issue #278

The mention_input_bar component requires these modifications to the CommandTextInput component of Makepad to work :Makepad PR #651

TODO for the future:

1. Add a header to the user list to display the current number of users in the room.
2. Implement scrolling functionality for the user list.
3. Enable sorting for the user list to show currently online users.
4. Optimize performance and add a loading animation for the user list.

[ZhangHanDong]

The current error in CI with cargo check is because the dependent CommandTextInput component has not been updated to the latest version.
This PR needs to be merged. Makepad PR #651

[alanpoon]

1. Mentionable List should not appear when only the "@" is being typed, it should appear only after "@ and some match characters"
2. There should be a header "Users" at the top of the mention-able List
3. Mentionable List seems to contain current user and does not contain one remaining room user.

The typing textbox needs to also be able to show avatar, after selecting the mentioned user.
5.

The typing textbox is not able to send the correct format for the mentioning the user. After mentioning the user, the message should show a hyperlink for the mentioned user.

https://github.com/user-attachments/assets/9f43e74e-7f0d-4ed6-a69c-322396f5a2af
The highlighted background by the mouse should be same color as default highlighted mentionable user/

7. In the mentionable List, the user_id should have a "@" at the front.

[ZhangHanDong]

1. Mentionable List should not appear when only the "@" is being typed, it should appear only after "@ and some match characters"
2. There should be a header "Users" at the top of the mention-able List
3. Mentionable List seems to contain current user and does not contain one remaining room user.

The typing textbox needs to also be able to show avatar, after selecting the mentioned user. 5. The typing textbox is not able to send the correct format for the mentioning the user. After mentioning the user, the message should show a hyperlink for the mentioned user.

https://github.com/user-attachments/assets/9f43e74e-7f0d-4ed6-a69c-322396f5a2af The highlighted background by the mouse should be same color as default highlighted mentionable user/

7. In the mentionable List, the user_id should have a "@" at the front.

I don’t quite understand the reason for the first point.

I will continue to address the suggestions 2/6/7.

The others can be considered as features to be added in the future. This is just the initial version.

[kevinaboos]

The current error in CI with cargo check is because the dependent CommandTextInput component has not been updated to the latest version. This PR needs to be merged. Makepad PR #651

the Makepad PR has been merged in now.

[ZhangHanDong]

Add a header and other modifications to the popup user list. But it depends on the new changes of the CommandTextInput component. PR 663.

[ZhangHanDong]

Currently, getting room members will cache a list locally. Is there any room for improvement in this solution? @kevinaboos

[kevinaboos]

Thanks, great start on this complex feature!

First, there are quite a few places where you're using chars/characters, e.g., in find_mention_trigger_position(). We can't use characters, we always must use unicode graphemes instead.

Second, I don't think we need a cache for the list of members in a room -- that's not something that is used frequently, so we shouldn't really cache it. The room user list will be cached internally by the client's EventCache, so we don't really want to cache it separately.
We can just store the latest list of Vec<RoomMember>s in the MentionInputBar's room_members field (and optionally, also in the TimelineUiState struct if needed), we don't need a full cache.

[kevinaboos]

I recently added support for an EditingPane that allows the user to edit messages. This EditingPane widget contains its own instance of the TextInput widget, which is completely separate from the message input_bar that you've modified here in this PR.

We need to support mentioning users in both the existing input_bar's TextInput at the bottom of the RoomScreen, and in the new edit_text_input TextInput within the EditingPane.

Can you refactor this PR to provide a MentionableTextInput widget that we can instantiate in multiple places? Then we can try it out in both the RoomScreen's input_bar and in the EditingPane's TextInput.

[ZhangHanDong]

@kevinaboos ok. I have processed your previous review suggestions, and next I will look at the EditingPane requirement.