Docs: retroactively document ConfigData->Sources renaming. (#8495)

Amend 4c0604e

docs/CHANGELOG.txt

@@ -64,6 +64,8 @@ Breaking changes:
 - Backends: Vulkan: Added 'uint32_t api_version' argument to ImGui_ImplVulkan_LoadFunctions().
   Note that it was also added to ImGui_ImplVulkan_InitInfo but for the later it is optional.
   (#8326, #8365, #8400)
+- Internals: Fonts: ImFontAtlas::ConfigData[] has been renamed to ImFontAtlas::Sources[],
+- Internals: Fonts: ImFont::ConfigData[], ConfigDataCount has been renamed to Sources[], SourceCount.
 - Internals: Menus: reworked mangling of menu windows to use "###Menu_00" etc. instead
   of "##Menu_00", allowing them to also store the menu name before it. This shouldn't
   affect code unless directly accessing menu window from their mangled name.

imgui.cpp

@@ -441,6 +441,7 @@ CODE
                             - old behavior altered border size (and therefore layout) based on border color's alpha, which caused variety of problems + old behavior a fixed 1.0f for border size which was not tweakable.
                             - kept legacy signature (will obsolete), which mimics the old behavior,  but uses Max(1.0f, style.ImageBorderSize) when border_col is specified.
                             - added ImageWithBg() function which has both 'bg_col' (which was missing) and 'tint_col'. It was impossible to add 'bg_col' to Image() with a parameter order consistent with other functions, so we decided to remove 'tint_col' and introduce ImageWithBg().
+ - 2025/02/25 (1.91.9) - internals: fonts: ImFontAtlas::ConfigData[] has been renamed to ImFontAtlas::Sources[]. ImFont::ConfigData[], ConfigDataCount has been renamed to Sources[], SourceCount.
  - 2025/02/06 (1.91.9) - renamed ImFontConfig::GlyphExtraSpacing.x to ImFontConfig::GlyphExtraAdvanceX.
  - 2025/01/22 (1.91.8) - removed ImGuiColorEditFlags_AlphaPreview (made value 0): it is now the default behavior.
                          prior to 1.91.8: alpha was made opaque in the preview by default _unless_ using ImGuiColorEditFlags_AlphaPreview. We now display the preview as transparent by default. You can use ImGuiColorEditFlags_AlphaOpaque to use old behavior.