Provide optional METIS support

* Split `CERES_NO_METIS` into two defines: `CERES_NO_PARTITION` and
  `CERES_NO_METIS`. The former refers to METIS support in SuiteSparse,
  the latter to the Eigen's MetisSupport module. This enables the use of
  sparse matrix reordering independent from SuiteSparse.
* Run Linux, macOS, and macOS Github workflows with METIS enabled
  SuiteSparse.

Fixes #808

Change-Id: I5076b7e1268d32cc3e7e56650edcbaf7fb3b59ce

.github/workflows/linux.yml

@@ -46,6 +46,7 @@ jobs:
             libgflags-dev \
             libgoogle-glog-dev \
             liblapack-dev \
+            libmetis-dev \
             libsuitesparse-dev \
             ninja-build
 

.github/workflows/macos.yml

@@ -48,6 +48,7 @@ jobs:
             gflags \
             glog \
             google-benchmark \
+            metis \
             ninja \
             suite-sparse
 

.github/workflows/windows.yml

@@ -92,12 +92,12 @@ jobs:
         uses: actions/cache@v2
         with:
           path: suitesparse/
-          key: ${{matrix.msvc}}-suitesparse-5.11.0-cmake.2-${{matrix.arch}}-${{matrix.build_type}}-${{matrix.lib}}
+          key: ${{matrix.msvc}}-suitesparse-5.12.0-cmake.3-${{matrix.arch}}-${{matrix.build_type}}-${{matrix.lib}}
 
       - name: Download SuiteSparse
         if: steps.cache-suitesparse.outputs.cache-hit != 'true'
         run: |
-          (New-Object System.Net.WebClient).DownloadFile("https://github.com/sergiud/SuiteSparse/releases/download/5.11.0-cmake.2/SuiteSparse-5.11.0-cmake.2-${{matrix.marker}}-Win64-${{matrix.build_type}}-${{matrix.lib}}-gpl.zip", "suitesparse.zip");
+          (New-Object System.Net.WebClient).DownloadFile("https://github.com/sergiud/SuiteSparse/releases/download/5.12.0-cmake.3/SuiteSparse-5.12.0-cmake.3-${{matrix.marker}}-Win64-${{matrix.build_type}}-${{matrix.lib}}-gpl-metis.zip", "suitesparse.zip");
           Expand-Archive -Path suitesparse.zip -DestinationPath ${{github.workspace}}/suitesparse;
 
       - name: Cache Eigen