feat: use forked neovim-qt with qt6 support

To build against Qt6 we need neovim-qt to support it. It is currently in
progress and will take some time.

Before that, we can use a fork with all the patches we need, while
contributing them upstream, if possible, and waiting for the main
project to be ready.

external/neovim-qt/CMakeLists.txt

@@ -3,23 +3,16 @@
 
 include(FetchContent)
 
-find_package(Git QUIET)
-
-file(GLOB NEOVIM_QT_PATCHES "${CMAKE_CURRENT_SOURCE_DIR}/patches/*.patch")
-
 FetchContent_Declare(
   neovimqt
-  GIT_REPOSITORY https://github.com/equalsraf/neovim-qt.git
-  GIT_TAG 3f05de82ecb5c1a24a7572081ae59e419eb059b8 # 0.2.17
-  PATCH_COMMAND ${GIT_EXECUTABLE} restore . && ${GIT_EXECUTABLE} apply ${NEOVIM_QT_PATCHES}
+  GIT_REPOSITORY https://github.com/gikari/neovim-qt.git
+  GIT_TAG c84f81712639140f910a1d38acb8edcb4509dc4d # qt6 branch
 )
 
 FetchContent_GetProperties(neovimqt)
 if(NOT neovimqt_POPULATED)
   FetchContent_Populate(neovimqt)
 
-  set(ENABLE_TESTS OFF CACHE INTERNAL "Turn off tests")
-
   # We use this, instead of MakeAvailable,
   # so that neovimqt is not installed in CI artifacts
   add_subdirectory(${neovimqt_SOURCE_DIR} ${neovimqt_BINARY_DIR} EXCLUDE_FROM_ALL)