Add ImGuiTreeNodeFlags_NoFrameOuterPadding flag

[RegimantasSimkus]

Added ImGuiTreeNodeFlags_NoFrameOuterPadding.

Why?
I've had a few different projects where I've used CollapsingHeader and have not been a fan of the way the edges of the header leak outwards onto the side, there is currently no real solution to this besides hacky approaches. The current logic is to add this 'outer padding' if the 'ImGuiTreeNodeFlags_Framed' is applied.

In my UIs when this collapsible header lives on a sidebar I don't think it looks very nice when its misaligned with contents.

Previous solution
My previous solution to this was to access window->WindowPadding and set it to (0, 0) for the TreeNodeEx/CollapsingHeader function call, but this solution is ugly and hacky.

	ImGuiWindow* window = GImGui->CurrentWindow;
	ImVec2 padding = window->WindowPadding;
	window->WindowPadding.x = window->WindowPadding.y = 0;
	bool configOpen = ImGui::CollapsingHeader("Configuration");
	window->WindowPadding = padding;

New solution

if (ImGui::CollapsingHeader("Configuration", ImGuiTreeNodeFlags_NoFrameOuterPadding))
{
}

Before

After
Nicely aligned

[RegimantasSimkus]

Dear.ImGui.DirectX9.Example.2026-01-19.19-36-44.mp4

[SuperRonan]

@RegimantasSimkus I have an unrelated question:
How did you make the 'Lorem ipsum' and 'Eos maiores' rectangular sections with a border and label?
I haven't found a way to do it in imgui and I was about to submit a PR with my own implementation of it until I randomly found your post.
I am very curious to know if their is already a way to do it.

[RegimantasSimkus]

@RegimantasSimkus I have an unrelated question: How did you make the 'Lorem ipsum' and 'Eos maiores' rectangular sections with a border and label? I haven't found a way to do it in imgui and I was about to submit a PR with my own implementation of it until I randomly found your post. I am very curious to know if their is already a way to do it.

custom component, it's a wrapper around BeginChild+padding and utilises ImGuiDrawList to draw the borders & title.

[SuperRonan]

custom component, it's a wrapper around BeginChild+padding and utilises ImGuiDrawList to draw the borders & title.

Thanks!
That's what I was suspecting (and is very close to my first impl before integrated it in the child window logic).