chore: add necessary imgui files for opengl3

feat: add glfw+opengl3 backend option to build.zig

feat: add backend impl for glfw+opengl3

chore: combine render() and draw() in backend

chore: handle all cases of enum

feat: add sdl2-opengl3 backend impl

fix: vcpkg stores SDL.h under SDL2 folder

macOS and Linux seem to not, so in order to get CI working again I
should make use of the preprocessor.

FIXME: I think this makes vcpkg a **hard** requirement which perhaps
isn't ideal if I want ZBA to be as easy to build as possible. I should
try ensuring that building w/out vcpkg works as well

chore: explicitly link SDL2

TODO: What happens on Windows? macOS?

feat: prefer SDL.h instead of SDL/SDL.h on all supported platforms

fix: restore import for glfw w/ opengl3 backend

rebase unalived that specific line. Whoops

fix: ensure that main.zig is removed

chore: Update to Zig v0.11.0

README.md

@@ -1,6 +1,6 @@
 # zgui v1.89.6 - dear imgui bindings
 
-Easy to use, hand-crafted API with default arguments, named parameters and Zig style text formatting. For a test application please see [here](https://github.com/michal-z/zig-gamedev/tree/main/samples/gui_test_wgpu).
+Easy to use, hand-crafted API with default arguments, named parameters and Zig style text formatting. [Here](https://github.com/michal-z/zig-gamedev/tree/main/samples/minimal_zgpu_zgui) is a simple sample application, and [here](https://github.com/michal-z/zig-gamedev/tree/main/samples/gui_test_wgpu) is a full one.
 
 ## Features
 
@@ -13,7 +13,7 @@ Easy to use, hand-crafted API with default arguments, named parameters and Zig s
 
 Copy `zgui` folder to a `libs` subdirectory of the root of your project.
 
-To get glfw/wgpu rendering backend working also copy `zgpu`, `zglfw` and `zpool` folders (see [zgpu](https://github.com/michal-z/zig-gamedev/tree/main/libs/zgpu) for the details). Alternatively, you can provide your own rendering backend, see: [backend_glfw_wgpu.zig](src/backend_glfw_wgpu.zig) for an example.
+To get glfw/wgpu rendering backend working also copy `zgpu`, `zglfw`, `zpool` and `system-sdk` folders (see [zgpu](https://github.com/michal-z/zig-gamedev/tree/main/libs/zgpu) for the details). Alternatively, you can provide your own rendering backend, see: [backend_glfw_wgpu.zig](src/backend_glfw_wgpu.zig) for an example.
 
 Then in your `build.zig` add:
 ```zig

build.zig

@@ -74,7 +74,9 @@ pub fn package(
     zgui_c_cpp.addIncludePath(.{ .path = thisDir() ++ "/libs" });
     zgui_c_cpp.addIncludePath(.{ .path = thisDir() ++ "/libs/imgui" });
 
+    const abi = (std.zig.system.NativeTargetInfo.detect(target) catch unreachable).target.abi;
     zgui_c_cpp.linkLibC();
+    if (abi != .msvc)
         zgui_c_cpp.linkLibCpp();
 
     const cflags = &.{"-fno-sanitize=undefined"};

src/gui.zig

@@ -2705,7 +2705,7 @@ extern fn zguiSetNextItemOpen(is_open: bool, cond: Condition) void;
 //--------------------------------------------------------------------------------------------------
 pub const SelectableFlags = packed struct(u32) {
     dont_close_popups: bool = false,
-    span_all_colums: bool = false,
+    span_all_columns: bool = false,
     allow_double_click: bool = false,
     disabled: bool = false,
     allow_item_overlap: bool = false,