The display name, filter string, and tooltips for the property editor (and associated detail customizations) are now stored as FText rather than FString. This allows us to remove SLATE_TEXT_ARGUMENT from the detail customization widgets.
[CL 2372595 by Jamie Dale in Main branch]
#ttp 330039 EDITOR: Platform-agnostic editor code depends on Windows-only VSAccessor headers
#detail Source code access is now extensible via plugins, so any new editors can be easily added.
#add Added SourceCodeAccess module that routes access via plugins.
#change Moved much of the old VSAccessor code into a new VisualStudioSourceCodeAccess plugin.
#add Added a counterpart XCode plugin & migrated the code from FSourceCodeNavigation (Applescript etc.) into there.
#remove Removed applescript for XCode access (it is now done via code).
#remove Removed source code access functionality from platform layer.
#add Added details customization for source code access settings, so users can choose their own accessor.
#remove Removed dependencies on VSAccessor.
#change Changed API in SWidget to not require building a string to be parsed, instead this acesses and forwards filenames & line numbers.
#extra Tested on Mac by Mark S.
reviewed by Andrew.Brown
[CL 2048697 by Thomas Sarkanen in Main branch]
