InputText: amends: now can use memchr()/strchr() for line counting. Much faster! (#7925)

docs/CHANGELOG.txt

@@ -63,6 +63,10 @@ Other changes:
      #6223, #6364, #6387, #6567, #6692, #6724, #6939, #6984, #7246, #7270, #7375, #7421, #7434,
      #7472, #7581, #7724, #7926, #7937 and probably more..)
 - Nav: pressing any keyboard key while holding Alt disable toggling nav layer on Alt release. (#4439)
+- InputText: internal refactoring to simplify and optimize the code. The ImWchar buffer has been
+  removed. Simplifications allowed to implement new optimizations for handling very large text buffers
+  (e.g. in our testing, handling of a 1 MB text buffer is now 3 times faster in VS2022 Debug build).
+  This is the first step toward more refactorig. (#7925) [@alektron, @ocornut]
 - InputText: added CJK double-width punctuation to list of separators considered for CTRL+Arrow.
 - TextLinkOpenURL(): modified tooltip to display a verb "Open 'xxxx'". (#7885, #7660)
 - Backends: SDL2: use SDL_Vulkan_GetDrawableSize() when available. (#7967, #3190) [@scribam]

docs/TODO.txt

@@ -65,7 +65,6 @@ It's mostly a bunch of personal notes, probably incomplete. Feel free to query i
  - selectable: generic BeginSelectable()/EndSelectable() mechanism. (work out alongside range-select branch)
  - selectable: a way to visualize partial/mixed selection (e.g. parent tree node has children with mixed selection)
 
- - input text: clean up the mess caused by converting UTF-8 <> wchar. the code is rather inefficient right now and super fragile. (WIP branch)
  - input text: preserve scrolling when unfocused?
  - input text: reorganize event handling, allow CharFilter to modify buffers, allow multiple events? (#541)
  - input text: expose CursorPos in char filter event (#816)