Improve expression type checking error for "match"

[anandthakker]

Using the following expression as a filter (using branch #5193 at the time of writing):

"filter": {
        "expression": [
          "curve",
          ["step"],
          ["zoom"],
          7,
          "all",
          8,
          [
            "<", [ "number", [ "get", "area" ] ], 80000
            ],
          9,
          [
            "<", [ "number", [ "get", "area" ] ], 20000
            ]
        ]
      }

Produces the error, filter.expression[6]: Expected String but found Boolean instead..

Ideally, the error would have been: filter.expression[4]: Expected Boolean but found String instead
With perhaps a secondary explanation: filter expressions must produce Boolean results
Even better filter.expression[4]: Expected Boolean but found String literal "all" instead

(h/t @aparlato @jfirebaugh )

[jmandel1027]

Hi @anandthakker is this bug still up for grabs?

Happy to work on it, so this looks like i'd need to update the error case on the expression/parsing_context to have have the improved error message which is evaluated by feature_filter/index.js at run time.

Just wanted to be sure i'm on the right track given the other work being done in this area. 👍

Thanks!