Change: add vcpkg.json to instruct vcpkg what dependencies we require

This works on all OSes, making it far simpler for any developer
to jump in. Just install vcpkg, run "vcpkg install" in our root,
and you have all the dependencies.

.github/workflows/ci-build.yml

@@ -135,9 +135,15 @@ jobs:
           zlib1g-dev \
           # EOF
 
-        sudo vcpkg install \
-          breakpad \
-          # EOF
+        echo "::group::Install vcpkg dependencies"
+
+        # Disable vcpkg integration, as we mostly use system libraries.
+        mv vcpkg.json vcpkg-disabled.json
+
+        # We only use breakpad from vcpkg, as its CMake files
+        # are a bit special. So the Ubuntu's variant doesn't work.
+        vcpkg install breakpad
+
         echo "::endgroup::"
       env:
         DEBIAN_FRONTEND: noninteractive
@@ -176,10 +182,15 @@ jobs:
 
     - name: Test
       run: |
-        cd build
-        ctest -j $(nproc) --timeout 120
+        (
+          cd build
+          ctest -j $(nproc) --timeout 120
+        )
 
-        # Check no tracked files have been modified
+        # Re-enable vcpkg.
+        mv vcpkg-disabled.json vcpkg.json
+
+        # Check no tracked files have been modified.
         git diff --exit-code
 
   macos:
@@ -208,17 +219,6 @@ jobs:
           core.exportVariable('ACTIONS_RUNTIME_TOKEN', process.env.ACTIONS_RUNTIME_TOKEN || '');
           core.exportVariable('VCPKG_BINARY_SOURCES', 'clear;x-gha,readwrite')
 
-    - name: Prepare vcpkg
-      run: |
-        vcpkg install --triplet=${{ matrix.arch }}-osx \
-          breakpad \
-          curl \
-          liblzma \
-          libpng \
-          lzo \
-          zlib \
-          # EOF
-
     - name: Install OpenGFX
       run: |
         mkdir -p ~/Documents/OpenTTD/baseset
@@ -283,17 +283,6 @@ jobs:
           core.exportVariable('ACTIONS_RUNTIME_TOKEN', process.env.ACTIONS_RUNTIME_TOKEN || '');
           core.exportVariable('VCPKG_BINARY_SOURCES', 'clear;x-gha,readwrite')
 
-    - name: Prepare vcpkg
-      shell: bash
-      run: |
-        vcpkg install --triplet=${{ matrix.arch }}-windows-static \
-          breakpad \
-          liblzma \
-          libpng \
-          lzo \
-          zlib \
-          # EOF
-
     - name: Install OpenGFX
       shell: bash
       run: |