tinywl: Add xdg-shell server as a dependency.

[Zeckmathederg]

Under some configurations when -D examples=true is passed to meson, ninja will fail to build the tinywl/tinywl.p/tinywl.c.o target because protocols_server_header['xdg-shell'] wasn't added as a source. tinywl/tinywl.p/tinywl.c includes xdg-shell-protocol.h which is generated from protocols_server_header['xdg-shell'], but if parallelism is too high, or when using samurai, since the dependency information is incomplete, the protocol server header won't generate before tinywl/tinywl.p/tinywl.c.o is attempted to be built, and will then proceed to fail.

This commit/PR fixes the issue for all configurations.

[WillPower3309]

Thanks for the PR! it looks good, but since upstream no longer contains those lines I think it's best to follow their path and remove them too.

[Zeckmathederg]

The server header will still be necessary, unless changed with wlroots-0.20.0. However, the client header shouldn't be necessary anymore, even with 0.19.x. So a simple replace with client to server will suffice here.

[Zeckmathederg]

I double checked with wlroots-0.20. Specifically, /usr/include/wlroots-0.19/wlr/types/wlr_xdg_shell.h includes xdg-shell-protocol.h which is expected to be generated by each build system individually. However, Wayland-Protocols now provides enum headers for most of the protocols. In the case of xdg-shell, this would be xdg-shell-enum.h. wlroots-0.20.x's wlr_xdg_shell.h now includes the enum header, which doesn't need to be generated by build systems.

So for now, I would recommend merging anyway, but this should be changed when wlroots-0.20 compatibility comes in.