Add xpath support for Problem Matcher

Describe the enhancement
Sniffing through logs using RegExp can be hairy especially if your need multiline line matching. In my particular use case I want to write a Problem Matcher for jest. The output from jest is very human friendly.

 FAIL  ./app.spec.js
  compare a and b
    ✕ should fail (7ms)

  ● compare a and b › should fail

    expect(received).toBe(expected) // Object.is equality

    Expected: "b"
    Received: "a"

      1 | describe('compare a and b', function() {
      2 |     it('should fail', function() {
    > 3 |         expect('a').toBe('b');
        |                     ^
      4 |     });
      5 | });
      6 |

      at Object.<anonymous> (app.spec.js:3:21)

Jest provides a CLI argument to print the test results in JSON. However, parsing this output using RegExp isn't that simple either.

What if the Problem Matcher API would allow us to use xpath to grep values from a json file on disc. Such an API would be useful and quite powerful addition.

Code Snippet

{
    "problemMatcher": [
        {
            "owner": "jest",
            "pattern": [
                {
                    "source": "./path/to/file.json",
                    "file": $.testResults[*].name,
                    "message": $.testResults[*].assertionResults[*].failureMessages
                }
            ]
        }
    ]
}

Start by locating the Problem Matcher API and reviewing how its current pattern configuration is parsed. The issue names no files or tests; done would require a decided design for extracting values from JSON files with XPath-like selectors, documented configuration behavior, and coverage for the proposed matching cases.