Backends: Vulkan: Added support for specifying multisample count. (#2705, #2706)

Synced/merged minor cruft from docking branch to minimize drift. AFAIK the only meaningful no-op change is that the call UpdateHoveredWindowAndCaptureFlags() was moved above UpdateMouseMovingNewFrame() to match what docking branch has been doing for a while.

Renamed ImGuiBackendFlags_HasVtxOffset to ImGuiBackendFlags_RendererHasVtxOffset to match naming convention already used in viewport/docking branch. (#2591) + Fix OpenGL3 code missing flag.

Examples/Backends: DirectX9/10/11/12, Vulkan, OpenGL3 (Desktop GL only): Added support for large meshes (64k+ vertices) with 16-bits indices, enable 'ImGuiBackendFlags_HasVtxOffset' config flag in back-end. (#2591)

Examples: Added missing per-renderer local changelogs. (#2037, #1639, #2452)

ImDrawCallback_ResetRenderState, Examples: Added support for reset render state callback. (#2037, #1639, #2452)

Vulkan: Bits. Using IM_ALLOC/IM_FREE instead of new[] / delete[].

Vulkan: Removed superfluous vkInstance parameters being passed along.

Vulkan: Removed requirement for user to pass their own render buffer storage to ImGui_ImplVulkan_RenderDrawData(), this is managed internally.

Vulkan: Added ImageCount to InitInfo structure (!= MinImageCount) will be needed for viewports. Renamed FramesQueueSize -> ImageCount. (#2472, #2071)

Vulkan, Viewports: Fix for resizing viewport windows crashing. (#2472)

Vulkan: Renaming demo/helper structures. Tidying up examples main.cpp.

Vulkan: Renaming, we want InitInfo to source MinImageCount which is the "source" value (so viewport creation can use this). Made ImGui_ImplVulkan_DestroyFrameRenderBuffers public. (#2071)

Vulkan: Storing user info into a single g_VulkanInitInfo structure to simplify code.

Vulkan: Added extra parameter to ImGui_ImplVulkan_RenderDrawData(). User is in charge of owning/storing 1 ImGui_ImplVulkan_FrameRenderBuffers per in-flight rendering frame. Removed ImGui_ImplVulkan_SetFramesQueueSize. (#2461, #2348, #2378, #2097, #2071, #1677)

Vulkan: More renaming. Comments.

Examples: Vulkan: Merged helpers into ImGui_ImplVulkanH_CreateWindowData. Removed ImGui_ImplVulkan_InvalidateFrameDeviceObjects from API. Comments. (#2071)

Examples: Vulkan: Renamed QueuedFramesCount to FramesQueueSize. Moved Framebuffer, Backbuffer to FrameData structure. (#2071)

Examples: Vulkan: Updated Changelog, removed debug code, tweaked code, made GLFW/SDL match each others. Initialize FrameDataForRender fields. Added Assertion. Clearing fields on DestroyFrameData(). (#2071)

Examples: Vulkan: Fixed tabs->space, removed extraneous braces and empty lines. (#2071)

Examples: Vulkan: Added calls to supports runtime changing back buffer count. (#2071)

Vulkan: Avoid passing negative coordinates to vkCmdSetScissor, which debug validation layers do not like.

Tabs to Spaces, comments.

Examples: Vulkan: Added shader sources/references in the .cpp source.

Examples: Vulkan: Using IM_ARRAYSIZE() where possible.

Examples: Vulkan: Added missing support for 32-bit indices (#define ImDrawIdx unsigned int). + demo typo

Examples: OpenGL3: Minor tweaks, clarifications + not calling glBindBuffer more than necessary in the render loop.

Examples: Vulkan: Rewrote scissor processing to match other examples more closely. Removed extraneous +1 of scissor extent height.

Examples: Vulkan: Support draw_data->FramebufferScale correctly matching a79785c for on Metal/GL2/GL3. (#2306, #1676)

ImDrawData: Added FramebufferScale field (currently a copy of the value from io.DisplayFramebufferScale). ...

This is to allow render functions being written without pulling any data from ImGuiIO, allowing incoming multi-viewport feature to behave on Retina display and with multiple displays. If you are not using a custom binding, please update your render function code ahead of time, and use draw_data->FramebufferScale instead of io.DisplayFramebufferScale. (#2306, #1676)
Examples: Metal, OpenGL2, OpenGL3: Fixed offsetting of clipping rectangle with ImDrawData::DisplayPos != (0,0) when the display frame-buffer scale scale is not (1,1). While this doesn't make a difference when using master branch, this is effectively fixing support for multi-viewport with Mac Retina Displays on those examples. (#2306) Also using ImDrawData::FramebufferScale instead of io.DisplayFramebufferScale.
Examples: Clarified the use the ImDrawData::DisplayPos to offset clipping rectangles.