Use a monospaced font for Influx QL query editor text areas

<!-- Please only use this template for submitting feature requests --> **Why is this needed**: The non-monospaced font used in query editor text areas makes it very easy to miss small characters like `.` or `,`.  These characters are much easier to read with a monospaced font:  It looks like this was done for Graphite at some point in #35515 but not for other editors. Besides, I _think_ (I don't have a Graphite datasource to verify this) that this got lost during the React migration in https://github.com/grafana/grafana/commit/0bf1a97262c6fd4d64dccd806147f58ba35de18b#diff-a0b3a6441314bac07df6a3c3b81d8e649c3cdd0dff9e35b11673ecf02f523a98R4-R53. **What would you like to be added**: All query editors (Graphite, Influx…) should use a monospaced font. **Who is this feature for?** Everyone using query editors.