Text Panel: Use bottom pane for text entry

**Why is this needed**: The text panel visualization does not utilize a datasource for rendering. Instead, users enter in text in the right side pane, and that text is shown in the visualization. Because of this, there is no bottom pane. With no bottom pane, we end up with a lot of unused space. The current input for the text panel being on the left means there is only a small window to enter text into, which is non-ideal **What would you like to be added**: We would like the bottom pane to show, but instead of the current datasource selector/query editor and transformation tabs, to include the text box used for inputting into the text panel. The current location of the text box in the side panel can be removed. Mock up: <img width="858" height="491" alt="Image" src="https://github.com/user-attachments/assets/f280fad7-c9c7-4e44-a22e-19581c582594" />