Fix missing reference to deprecated TreeAdvanceToLabelPos

Hook up the function arguments to ImGuiContext that allow us to share texture atlases, and make the textureById cache global, se we share those font textures across contexts.

add ImGuiIO backend info

v1.71

move drag/drop payload data into script

v1.67

v1.66

v1.65

Fix utf-8 encoding issues

v1.63

use typed array set instead of emscripten::vecFromJSArray

update to Emscripten 1.38.10; fix compiler warnings; update npm packages

clean up using import/export/access templates

import_number_or_null for float

import/export number; import ImVec2/ImVec4 or null

clean up code with some macros

wrap ImGuiContext; move global variables

use opaque pointers for ImGuiContext

utf-8 support

AddFontFromMemoryTTF needs a native copy of the data

use optional_override instead of select_overload for lambda functions

fix indentation

change strcpy to strncpy

more font support; add fonts to style editor in demo

use raw pointer for ImGuiContext

move and rename all static globals

label reference get/set functions

remove some unused raw pointers

use references for ImGuiTextEditCallbackData and ImGuiSizeCallbackData

remove constructors for ImVec2 and ImVec4