Manual overloads for ImGui functions accepting text (#2319)

* wip2

* Implement AutoUtf8Buffer

* reformat

* Work on manual bindings

* restructure

* Name scripts properly

* Update utility functions to use ImU8String

* add overloads

* Add more overloads

* Use ImGuiWindow from gen, support AddCallback

* Use LibraryImport for custom ImGuiNative functinos

* Make manual overloads for string-returning functinos

* Make all overloads with self as its first parameter extension methods

* Fix overload resolution by removing unnecessary

* in => scoped in

* Fix compilation errors

imgui/Dalamud.Bindings.ImGui/Custom/ImGuiTextBuffer.Custom.cs

@@ -0,0 +1,26 @@
+using System.Runtime.CompilerServices;
+using System.Text;
+
+namespace Dalamud.Bindings.ImGui;
+
+public unsafe partial struct ImGuiTextBuffer
+{
+    public readonly Span<byte> Span => new(this.Buf.Data, this.Buf.Size);
+
+    public override readonly string ToString() => Encoding.UTF8.GetString(this.Span);
+
+    public void append(ImU8String str)
+    {
+        fixed (ImGuiTextBuffer* thisPtr = &this)
+            ImGui.append(thisPtr, str);
+    }
+}
+
+public unsafe partial struct ImGuiTextBufferPtr
+{
+    public readonly Span<byte> Span => new(Unsafe.AsRef(in this).Buf.Data, Unsafe.AsRef(in this).Buf.Size);
+
+    public override readonly string ToString() => Encoding.UTF8.GetString(this.Span);
+
+    public void append(ImU8String str) => ImGui.append(this, str);
+}