Add problem matchers for Github actions

- Add a basic problem matcher for illuaminate errors.
 - Add a script (tools/parse-reports.py) which parses the XML reports
   generated by checkstyle and junit, extracts source locations, and
   emits them in a manner which can be consumed by another set of
   matchers.

This should make it a little easier to see problems for folks who just
rely on CI to test things (though also, please don't do this if you can
help it).

.github/workflows/main-ci.yml

@@ -41,8 +41,11 @@ jobs:
         path: build/libs
 
     - name: Upload Coverage
-      run: bash <(curl -s https://codecov.io/bash)
-      continue-on-error: true
+      uses: codecov/codecov-action@v1
+
+    - name: Parse test reports
+      run: ./tools/parse-reports.py
+      if: ${{ failure() }}
 
     - name: Cache pre-commit
       uses: actions/cache@v2
@@ -51,6 +54,7 @@ jobs:
         key: ${{ runner.os }}-pre-commit-${{ hashFiles('config/pre-commit/config.yml') }}
         restore-keys: |
           ${{ runner.os }}-pre-commit-
+
     - name: Run linters
       run: |
         pip install pre-commit