File path case-insensitivity on Windows

[martincohen]

As requested by @isidorn, I'm filing this issue separately.

The issue of case-insensitivity on Windows is basically breaking everything with my experience in C/C++ development, especially when using MSVC toolchain. I have duplicate files opened most of the time (that are not with same path according to vscode, therefore they function as two distinct files):

The problem often (like every 5 minutes) results in this:

Which in turn results in a lot of changes being lost, or serious time waste in trying to merge the two files.

In my humble opinion, this is a major issue in the vscode core for anyone trying to use Windows-only command-line tools. And so it is a problem for extension creators on Windows, as they are required to be extra careful with case-sensitivity required currently by vscode, which does not follow platform guidelines for handling paths.

Also it is very easy to get to this state (using MSVC cppvsdbg), which is the biggest problem:

1. Open a file from Explorer.
2. One of the following:
   a. Put breakpoint to a C/C++ file. Run debug and get a new file instance each time you step (so even if you close it, the next step will reopen the same file).
   c. Open an issue from Problems view and get a new file instance.
   d. Open a file from external application with different case in the path (cmd, Total Commander, etc.) and get a new file instance.

In fact you can have dozens of instances of the same file.

[bpasero]

Duplicate of #12448

[bpasero]