Add ForceCloseButton TabItem flag

[tpecholt]

Version/Branch of Dear ImGui:

Version 1.91.6, Branch: docking

Back-ends:

glfw + opengl3

Compiler, OS:

MSVC 2022

Full config/build information:

No response

Details:

My Issue/Question:

Currently a tab item shows close button only when hovered. In many applications close buttons are showed permanently so it would be nice to support this with an additional flag e.g. ImGuiTabItemFlags_ForceCloseButton.

Screenshots/Video:

Minimal, Complete and Verifiable Example code:

ImGui::BeginTabItem("tab", &isOpen)

[ocornut]

If anything it would likely be a style settings rather than a per-tab item flag.