MDEV-12386: Use AppVeyor for public Windows CI

Signed-off-by: Daniel Black <daniel.black@au.ibm.com>

appveyor.yml

+version: 10.2-{build}
+before_build:
+- md %APPVEYOR_BUILD_FOLDER%\win_build
+- cd %APPVEYOR_BUILD_FOLDER%\win_build
+- cmake ..  -G "Visual Studio 15 2017" -DBOOST_ROOT=C:\Libraries\boost_1_64_0 -DPKG_CONFIG_EXECUTABLE=C:\perl\bin\pkg-config -DBISON_EXECUTABLE=C:\cygwin\bin\bison
+- dir
+build:
+  project: win_build\MySQL.sln
+  parallel: true
+  verbosity: minimal
+configuration:
+  - Debug
+test:
+test_script:
+- cd %APPVEYOR_BUILD_FOLDER%\win_build\mysql-test
+- perl mysql-test-run.pl --force --max-test-fail=20 --parallel=6 --testcase-timeout=2 --skip-test-list=unstable-tests --suite=main,innodb,plugins,mariabackup
+image: Visual Studio 2017