CI: Use Visual Studio 2019 instead of 2017

Visual Studio 2019 brings C11 support and is actually needed (or best
suited at least) if we are:

* Building with debugging code enabled (/Zc:preprocessor is required)
* Introspection works better on Visual Studio 2019 or later, also due to
  the preprocessor improvements.
* Pulling in bleeding edge Cairo (and possibly soon, GLib) already
  requires C11 support.

.gitlab-ci.yml

@@ -264,7 +264,7 @@ macos:
     paths:
       - "${CI_PROJECT_DIR}/_build/meson-logs"
 
-vs2017-x64:
+vs2019-x64:
   # TODO: Uncomment this when ready to merge.
   # rules:
   #   - if: $CI_PROJECT_NAMESPACE == "GNOME"

.gitlab-ci/test-msvc.bat

@@ -1,7 +1,7 @@
 @echo on
 :: vcvarsall.bat sets various env vars like PATH, INCLUDE, LIB, LIBPATH for the
 :: specified build architecture
-call "C:\Program Files (x86)\Microsoft Visual Studio\2017\BuildTools\VC\Auxiliary\Build\vcvarsall.bat" x64
+call "C:\Program Files (x86)\Microsoft Visual Studio\2019\BuildTools\VC\Auxiliary\Build\vcvarsall.bat" x64
 @echo on
 
 pip3 install --upgrade --user meson~=1.2 || goto :error