addpkg(x11/luanti{-common,-server}): moved from TUR

Copied and pasted from https://github.com/termux-user-repository/tur/tree/master/tur/luanti

Previous documentation here:
- termux-user-repository/tur#1295
- termux-user-repository/tur#1296
- termux-user-repository/tur#1331
- termux-user-repository/tur#1327

Summary of key points:

- for better performance than normal virglrenderer-android, test using [termux-wsi-layer](#22353) or [new virglrenderer](#22385)

- to use touchscreen input, set "Touchscreen input mode: Direct touch" in Termux:X11 settings

- to use keyboard input, set "Prefer scancodes" in Termux:X11 settings

- to use mouse input, set "Capture external pointer devices" in Termux:X11 settings

- 6 patches are unique to TUR/termux, but the patch 0001-enable-egl-without-sdl2.patch is
  a cherry pick of minetest/minetest@4838eb2

x11-packages/luanti/0002-fix-elf-directory-for-cross-compiling.patch

@@ -0,0 +1,28 @@
+Normally, Luanti does not set the EXECUTABLE_OUTPUT_PATH variable when cross-compiling is detected,
+because Luanti does not officially cross-compile for any platforms that require EXECUTABLE_OUTPUT_PATH.
+
+Later on elsewhere in the CMakeLists.txt, there is this logic: "if not ANDROID... then if UNIX...
+then create a symlink in the EXECUTABLE_OUTPUT_PATH".
+
+https://github.com/minetest/minetest/blob/6a1d22b2c516abbb9ce9670dedff47451317706f/src/CMakeLists.txt#L1045-L1054
+
+A different patch, 0003-bionic-libc-x11-wsi-opengl-es-2.patch, replaces the ANDROID variable there 
+to force this codepath, but the reason this patch is not combined into that patch is because this patch
+is technically only required for cross-compiling,
+while building the package in non-cross-compiling mode does not actually require this
+change in order to work, so it seemed appropriate to organize them in separate patches.
+
+This prevents the error "CMake Error: failed to create symbolic link '/minetest': Permission denied",
+which is the error that happens if EXECUTABLE_OUTPUT_PATH does not exist when that linked point
+in the CMakeLists.txt is reached, and normally happens only when cross-compiling Luanti.
+--- a/src/CMakeLists.txt
++++ b/src/CMakeLists.txt
+@@ -569,7 +569,7 @@ endif()
+
+ # When cross-compiling assume the user doesn't want to run the executable anyway,
+ # otherwise place it in <source dir>/bin/ since Luanti can only run from there.
+-if(NOT CMAKE_CROSSCOMPILING)
++if(NOT DISABLING_THIS_BECAUSE_IT_IS_FOR_BUILDING_AN_APK)
+ 	set(EXECUTABLE_OUTPUT_PATH "${CMAKE_SOURCE_DIR}/bin")
+ endif()
+