Selectable: Fixed horizontal label alignment when combined with using ImGuiSelectableFlags_SpanAllColumns. (#8338)

Windows, Style: Fixed small rendering issues with menu bar, resize grip and scrollbar when using thick border sizes. (#8267, #7887)

Amend e.g. 742b5f4c.

ColorEdit, ColorPicker: (Breaking) redesigned how alpha is displayed in the preview square. (#8335, #1578, #346)

Added ImGuiColorEditFlags_AlphaOpaque, ImGuiColorEditFlags_AlphaNoBg.
Removed ImGuiColorEditFlags_AlphaPreview.

Backends: SDL_GPU: shallow tweaks + disable anisotropy in sampler. Examples: SDL+Vulkan: Fixed incorrect defines.

Moved ImGuiColorEditFlags_AlphaPreview/ImGuiColorEditFlags_AlphaPreviewHalf flags. Demo: reorganized some of color edit/picker demo section.

ImAlphaBlendColors() was broken by ImLerp() change. (cd6c83cd)

Unlikely to meaningful affect anyone but still..

Backends: SDL2,SDL3: removed assert preventing using ImGui_ImplSDL2_SetGamepadMode()/ImGui_ImplSDL3_SetGamepadMode() with ImGui_ImplSDL2_GamepadMode_Manual/ImGui_ImplSDL3_GamepadMode_Manual and an empty array. (#8329)

Font: Internals: make used page maps smaller. Since it's extremely rarely used and for iterations only. ~34->16 bytes with ImWchar32.

Windows: latch FontRefSize at time of Begin(), consistent with e.g. TitleBarHeight, and to avoid calling CalcFontSize() on non-current window.

Windows: legacy SetWindowFontScale() is properly inherited by nested child windows. (#2701, #8138, #1018)

Backends: SDLGPU3: Rename GpuDevice->Device. Expose ImGui_ImplSDLGPU3_CreateDeviceObjects(), ImGui_ImplSDLGPU3_DestroyDeviceObjects(). Misc renaming. (#8163, #7998, #7988)

Examples: Vulkan: vkAcquireNextImageKHR() and vkQueuePresentKHR() returning VK_SUBOPTIMAL_KHR keeps moving forward. (#7825, #7831)

Examples: DirectX12: Reduced number of frame in flight from 3 to 2 in provided example, to reduce latency.

Backends: DirectX12: Texture upload use the command queue provided in ImGui_ImplDX12_InitInfo instead of creating its own.

+ minor tweaks to faciliate branch merging.