Generate and build with Visual Studio 2019 GUI

[inkydragon]

I mean that the VS 2019 project can be generated by meson --backend=vs2019, and then compiling and debugging using its GUI.

The output VS 2019 project files still have some bugs, here are some workarounds:

1. Generate VS 2019 project: meson -Ddefault_library=static --force-fallback-for=zlib,harfbuzz,freetype2,fribidi,libpng -Dfreetype2:harfbuzz=disabled -Dharfbuzz:freetype=disabled -Dharfbuzz:cairo=disabled -Dharfbuzz:glib=disabled -Dharfbuzz:gobject=disabled --backend=vs2019 build-vs2019
2. Replace some path: Replace "subprojects\ffmpeg => "..\..\subprojects\ffmpeg in all *.vcxproj files in the build directory (build-vs2019\).
   In my case: 136 times to replace in 6 files (build-vs2019-test\subprojects\ffmpeg\8fd69c1@@????@sta.vcxproj)
3. Open Aegisub.sln and build

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All those wrong paths in step 2 are using by CustomBuild, source files usually are *.asm.
Maybe is an upstream bug about custom build.

[CoffeeFlux]

It's an issue in Meson itself, reported here: mesonbuild/meson#8020