[Feature Request]: Allow other extensions / commands to read / trigger from results grid

Often my workflow involves running a query and following up with more investigation into certain rows of the query. I've written my own extension that allows me to launch certain programs passing in selected text from the editor as a parameter.

Example:
```json
{
"key": "ctrl+shift+s",
"command": "snapCommandExtension.runSnap",
"when": "editorHasSelection"
},
```
What I'd like to be able to do is to have this run from the result grid instead, so that I could select a cell (or cells) and execute my command.

Start by locating the result grid entry points and the command/keybinding integration described in the issue. Investigate how selected cells are exposed, then verify that a configured extension command can be triggered with the selected cell or cells as input.

Written by the indexing model from the issue text.