feat: Implement mouse text selection support

[dklassic]

Currently text selection only works with keypress and implementing mouse text selection support would be a great improvement. This feature will have to be added in through Servo, some upstream issues are currently tracking part of our requirement:

• No blinking cursor in editable elements servo/servo#33237
• layout: implement process_text_index_request servo/servo#35432

Meanwhile Servo already had both edit point and text selection functionality implemented in htmlinputelement and htmltextareaelement respectively, what's left to do is to actually display it in a visible manner. Additionally mouse selection on htmlinputelement has already been implemented albeit currently the layout engine simply does not respond to query.

Expected Behavior:

Users should be able to click on text, see a caret at where they've clicked on, and see the text being selected by dragging a mouse click.

Acceptance Criteria:

• The text input interface should show a caret at where the edit point is at
• The text input interface should show where the range of text selected
• When clicking on text inside a text input, the edit point should be updated to the closest location within the text from where the mouse click happened

Good to Haves:

• Currently the mouse selection implementation is only done for the htmlinputelement but would be nice to have it extended to htmltextareaelement as well