Add dub.selections.json, upgrade libdparse 0.22.0

Note: currently a warning is emitted when building, because dscanner now
depends on libdparse 0.22.0, but dsymbol doesn't support it officially
yet. We just force it with dub.selections.json to build with 0.22.0 for
executable builds.

.github/workflows/default.yml

@@ -40,6 +40,7 @@ jobs:
         ]
         build: [
           { type: make },
+          { type: dub, version: 'current' },
           { type: dub, version: 'min libdparse' },
           # Fail due to unresolvable dependencies
           # { type: dub, version: 'max libdparse' },
@@ -104,14 +105,22 @@ jobs:
 
       # Compile D-Scanner and execute all tests using a specific dependency version
       # Currently skipped for GDC (dub installed from apt-get is broken)
-      - name: Build and test with dub
-        if: ${{ matrix.build.type == 'dub' }}
+      - name: Build and test with dub (min or max libdparse test)
+        if: ${{ matrix.build.type == 'dub' && matrix.build.version != 'current' }}
         env:
           DC: ${{ matrix.compiler.dmd }}
         run: |
           rdmd ./d-test-utils/test_with_package.d ${{ matrix.build.version }} -- dub build
           rdmd ./d-test-utils/test_with_package.d ${{ matrix.build.version }} -- dub test
 
+      - name: Build and test with dub (with dub.selections.json)
+        if: ${{ matrix.build.type == 'dub' && matrix.build.version == 'current' }}
+        env:
+          DC: ${{ matrix.compiler.dmd }}
+        run: |
+          dub build
+          dub test
+
       - uses: actions/upload-artifact@v2
         with:
           name: bin-${{matrix.build.type}}-${{matrix.build.version}}-${{ matrix.compiler.dmd }}-${{ matrix.host }}