[Build] Simplify download of API Tools matcher in shared GH workflow

Makes it more compact and only relays on tools provided by the runner.
Additionally adapt the defined 'api-problems' problem-matcher to the new
console printout.

Author: HannesWell

.github/matcher/api-tools.json

@@ -4,7 +4,7 @@
       "owner": "api-problems",
       "pattern": [
         {
-          "regexp": "^\\[API\\s(\\w+)\\].*line\\s(\\d+):\\s(.+)\\(location:\\s(.+)\\)$",
+          "regexp": "\\[API (ERROR|WARNING)\\].* at line (\\d+):\\s(.+)\\(location:\\s(.+)\\)$",
           "severity": 1,
           "line": 2,
           "message": 3,

.github/workflows/mavenBuild.yml

@@ -85,12 +85,10 @@ jobs:
         tycho-version: 4.0.12
 
     - name: Download the API Tools matcher
-      uses: suisei-cn/actions-download-file@818d6b7dc8fe73f2f924b6241f2b1134ca1377d9 # v1.6.0
-      id: api-tools-matcher
-      with:
-        url: "https://raw.githubusercontent.com/eclipse-platform/eclipse.platform.releng.aggregator/master/.github/matcher/api-tools.json"
-        target: .github/matcher
-    - run: echo "::add-matcher::.github/matcher/${{ steps.api-tools-matcher.outputs.filename }}"
+      run: |
+        mkdir .github/matcher
+        curl -o .github/matcher/api-tools.json https://raw.githubusercontent.com/eclipse-platform/eclipse.platform.releng.aggregator/master/.github/matcher/api-tools.json
+        echo "::add-matcher::.github/matcher/api-tools.json"
     - name: Build with Maven
       run: >-
         ${{ runner.os == 'Linux' && 'xvfb-run' || '' }}