Query editor: execute highlighted text, from cursor, and current batch

[erikdarlingdata]

Feature Request

Add SSMS-style query execution options to the query editor:

1. Execute highlighted text only — if text is selected, only execute the selection instead of the entire editor contents
2. Execute from cursor position — execute from the current cursor position to the end of the editor
3. Execute current batch — execute only the batch (text between GO batch separators) where the cursor is currently positioned. This should match SSMS behavior:
   • GO is a batch separator, not a T-SQL command
   • GO must be on its own line (optionally with whitespace)
   • Each batch between GO separators is an independent unit of execution

These are standard features in SSMS and other SQL editors that users expect when working with multi-batch scripts.