Make no attempt to replicate the depot layout.
Unicode non-characters [1] are guaranteed to never be used for a character. The formerly used U+fffd however is a valid character - the replacement character [2] correctly displayed by Qt5 as <?>. [1] https://en.wikipedia.org/wiki/Universal_Character_Set_characters#Non-characters [2] https://en.wikipedia.org/wiki/Specials_(Unicode_block)#Replacement_character Issue #3483
This patch adds a simple UTF-8 decoder at 'os/include/util/utf8.h' along with a test at 'os/run/utf8.run'. Fixes #2717, related to issue #2716