FR: Add a blinking cursor for uiTextInput when user clicks on it

Currently when u click in the input, no blinking cursor appears so it's not clear if it's currently being focused on.

Example when I click the text input for "Login" (no blinking cursor so u can't tell):

Start by locating the uiTextInput implementation and reproduce the reported Login input behavior by clicking into it. Trace how focus is represented, then make completion observable by verifying that a blinking cursor appears while the input is focused and disappears when it is not.

Written by the indexing model from the issue text.