Show loading indicator when query is executed

### Feature Description

After a query is executed and before results are returned, the bottom pane displays no results.

Proposed redesign: Show a loading indicator (e.g., status bar, spinning wheel) to indicate that the query is still running, instead of displaying a "no results" message. The current design causes confusion, particularly when the query takes longer to complete.

### Problem and Motivation

see above

### Related Area

- [ ] Connection dialog (SQL Server | Azure browse/Fabric browse)
- [x] Query editor
- [ ] Query results panel
- [ ] Object Explorer
- [ ] GitHub Copilot integration
- [ ] Preview/Edit data
- [ ] Table Designer
- [ ] Schema Designer
- [ ] Schema Compare
- [ ] Local SQL Server Container provisioning
- [ ] SQL database in Fabric provisioning
- [ ] DACPAC/BACPAC export/import
- [ ] SQL Database projects
- [ ] Query Plan Visualizer
- [ ] Other (please describe below)

### If you selected "Other", please describe the area

_No response_

### Confirmation

- [x] I have searched existing feature requests and couldn't find a match
- [ ] I want to help implement this feature

Start by locating the query editor's query-execution flow and the state that currently displays the bottom pane's "no results" message. Trace how execution begins and results return, then add a loading indication for the waiting period and verify that the no-results state is not shown prematurely.

Written by the indexing model from the issue text.