This restores Windows platform file handling back to open files non-exlusively by default, as was the case before October 2018. (See b902a2f2a7)
Back then, while fixing warnings for MSVC, the function used for opening files was changed from _wfopen() to _wfopen_s() as suggsted by the warning C4996. ("This function may be unsafe, consider using _wfopen_s instead.")
This new function
1. did parameter validation and thus avoided some possible security issues due to nil pointers or wrongly terminated strings
2. it also changed the default file sharing for opened files from _SH_DENYNO (which was the implicit default for the previous _wfopen()) to _SH_SECURE.
_SH_DENYNO means every opened file could be opened by other calls (like is the default on other operating systems).
_SH_SECURE means if the file is opened with READ access, others can still read the same file, but if it is opened with WRITE access, others can't open it at all, not even to read.
This led to rarely occuring bugs on Windows, i.e. due to random access by Antivirus processes, or Godot/Windows not closing a file handle fast enough while trying to open it again elsewhere (i.e. project.godot, instead showing the Project manager, or saving shaders/debugging the game).
What this PR does it change the file access to a third method, _wfsopen(). This is still secure, doing parameter validation and thus avoids the warning, but it allows us to actually SET the file sharing parameter. And we set it to _SH_DENYNO, as it was implicitely before the change. (And as it currently is on all non-Windows platforms, where file sharing restrictions don't exist by default.)
Warning C4996 should really have been pointing this out. It should've been _wfsopen() all along. Let's hope this banishes those annoying, rare errors for all eternity.
Fixes#28036.
(cherry picked from commit b48cbb5da9)
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