build: annotate markdown lint failures in pull requests

Add a problem matcher for output from remark-lint to our lint-md GitHub
Actions CI workflow so that any markdown linter failures are annotated
in the pull request in the web UI.

Signed-off-by: Richard Lau <riclau@uk.ibm.com>

PR-URL: #32391
Refs: https://github.com/actions/toolkit/blob/master/docs/problem-matchers.md
Refs: https://github.com/actions/toolkit/blob/master/docs/commands.md#problem-matchers
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>
Reviewed-By: Matheus Marchini <mat@mmarchini.me>

.github/workflows/CI.yml

@@ -64,7 +64,9 @@ jobs:
       with:
         node-version: 10.x
     - name: Lint docs
-      run: NODE=$(which node) make lint-md
+      run: |
+        echo "::add-matcher::.github/workflows/remark-lint-problem-matcher.json"
+        NODE=$(which node) make lint-md
   lint-js:
     runs-on: ubuntu-latest
     steps:

.github/workflows/remark-lint-problem-matcher.json

@@ -0,0 +1,22 @@
+{
+  "problemMatcher": [
+    {
+      "owner": "remark-lint",
+      "pattern": [
+        {
+          "regexp": "^(?:\\x1b\\[\\d+m)*(.+?)(?:\\x1b\\[\\d+m)*$",
+          "file": 1
+        },
+        {
+          "regexp": "^\\s+(?:\\d+:\\d+-)?(\\d+):(\\d+)\\s+\\S*(error|warning|info)\\S*\\s+(.+)\\s+(\\S+)\\s+(?:\\S+)$",
+          "line": 1,
+          "column": 2,
+          "severity": 3,
+          "message": 4,
+          "code": 5,
+          "loop": true
+        }
+      ]
+    }
+  ]
+}