ImDrawData: changed CmdLists from raw array to ImVector<> owned by ImDrawData itself. Faclitate user-manipulation of the array (#6406, #4879, #1878) + deep swap. (#6597, #6475, #6167, #5776, #5109, #4763, #3515, #1860)

+ Metrics: avoid misleadingly iterating all layers of DrawDataBuilder as everything is flattened into Layers[0] at this point.

# Conflicts:
#	imgui.cpp
#	imgui_internal.h

docs/CHANGELOG.txt

@@ -39,9 +39,20 @@ Breaking changes:
 - IO: Obsoleted io.ClearInputCharacters() (added in 1.47) as it now ambiguous
   and often incorrect/misleading considering the existence of a higher-level
   input queue. (#4921)
+- ImDrawData: CmdLists[] arra is now owned, changed from 'ImDrawList**' to
+  'ImVector<ImDrawList*>'. Majority of users shouldn't be affected, but you
+  cannot compare to NULL nor reassign manually anymore.
+  Instead use AddDrawList(). (#6406, #4879, #1878)
 
 Other changes:
 
+- ImDrawData: CmdLists[] array is now an ImVector<> owned by ImDrawData rather
+  than a pointer to internal state.
+  - This makes it easier for user to create their own or append to an existing draw data.
+    (#6406, #4879, #1878)
+  - This makes it easier to perform a deep-swap instead of a deep-copy, as array
+    ownership is now clear. (#6597, #6475, #6167, #5776, #5109, #4763, #3515, #1860)
+  - Syntax and allocation count are otherwise identical.
 - Fixed CTRL+Tab dimming background assert when target window has a callback
   in the last ImDrawCmd. (#4857, #5937)
 - InputText: Fixed a case where deactivation frame would write to underlying