Renderer: Add a way to highlight a particular column

[lloydtabb]

What happens?

run: order -> {
  group_by:
     product
  aggregate:
     total_revenue
     # highlight
      order_count
 }

### To Reproduce

something

### OS:

all

### Malloy Client:

render

### Malloy Client Version:

all

### Database Connection:

all

[tschomer]

lets please hold a bit on this... i'm working on bigger picture table/results stuff.