[build] Update to Doxygen 1.9.1 (#3008)

.github/workflows/documentation.yml

@@ -18,6 +18,8 @@ jobs:
       - uses: actions/setup-java@v1
         with:
           java-version: 13
+      - name: Install libclang-9
+        run: sudo apt update && sudo apt install -y libclang-cpp9 libclang1-9
       - name: Set environment variables (Development)
         run: |
           echo "TARGET_FOLDER=$BASE_PATH/development" >> $GITHUB_ENV

.github/workflows/gradle.yml

@@ -103,6 +103,8 @@ jobs:
       - uses: actions/setup-java@v1
         with:
           java-version: 13
+      - name: Install libclang-9
+        run: sudo apt update && sudo apt install -y libclang-cpp9 libclang1-9
       - name: Set release environment variable
         run: echo "EXTRA_GRADLE_ARGS=-PreleaseMode" >> $GITHUB_ENV
         if: startsWith(github.ref, 'refs/tags/v')

docs/build.gradle

@@ -39,7 +39,7 @@ cppProjectZips.add(project(':wpilibNewCommands').cppHeadersZip)
 
 doxygen {
     executables {
-        doxygen version : '1.8.18',
+        doxygen version : '1.9.1',
         baseURI : 'https://frcmaven.wpi.edu/artifactory/generic-release-mirror/doxygen'
     }
 }