Port from master to RB-2.1 - Fixes Unicode paths on Windows (#1363)

[hodoulp]

• Fixes Unicode paths on Windows

Unlike most other platforms, Windows' Unicode is standardized around
UTF-16, an encoding not compatible with "char *" arrays common in
C/C++. As such, to support Unicode correctly when using Win32 APIs,
strings must be converted to and from UTF-16 and the Unicode
versions of the APIs must be used over the ANSI versions.

This commit introduces the following:

• Utility funcions for converting between UTF-8 and UTF-16LE on all
  platforms:

  • Platform::Utf8ToUtf16
  • Platform::Utf16ToUtf8

• Adds test for these conversion functions to ensure the conversion
  to and from UTF-8 and UTF-16LE is correct.

• Utility wrappers for "std::ifstream" that automatically convert
  to and from UTF-16 so that filenames requiring Unicode encoding
  function correctly:

  • Platform::CreateInputFileStream
  • Platform::OpenInputFileStream

• Moves the file default compute hash function to the Platform
  class (Platform::CreateFileContentHash) and switches to the
  Win32 UTF-16 variant on Windows.

• Adds the "UNICODE" macro before including "Windows.h" which
  ensures all functions called are the Unicode variants instead of
  the default ANSI variants.

  • Implicitly changes functions such as GetEnvironmentVariable and
    SetEnvironmentVariable to their Unicode variants.

• Changes the following environment variable related functions to
  their Win32 Unicode variants on Windows:

  • environ -> _wenviron
  • _putenv_s -> _wputenv_s

• Updates tests using SetEnvironmentVariable to use wide string
  literals since that function has been switched to the Unicode
  variant.

Signed-off-by: itsmattkc itsmattkc@gmail.com

• Moved UNICODE and _UNICODE definitions to CMake

Signed-off-by: itsmattkc 34096995+itsmattkc@users.noreply.github.com

• handle empty strings and use const references

Signed-off-by: itsmattkc 34096995+itsmattkc@users.noreply.github.com

• only use wenviron when unicode is enabled

Signed-off-by: itsmattkc itsmattkc@gmail.com

• add ANSI Win32 version of Getenv

Signed-off-by: itsmattkc itsmattkc@gmail.com

• Add CMake option for compiling with Win32 Unicode support

Signed-off-by: itsmattkc itsmattkc@gmail.com

• Throw exception if UTF functions are called on non-Windows platforms

Signed-off-by: itsmattkc itsmattkc@gmail.com

• Throw OCIO Exception

Signed-off-by: itsmattkc itsmattkc@gmail.com

• Don't run UTF-8/16 conversion test on non-Windows

Signed-off-by: itsmattkc 34096995+itsmattkc@users.noreply.github.com

• Fix CMake error

Signed-off-by: itsmattkc 34096995+itsmattkc@users.noreply.github.com

• minor CMake adjustment

Signed-off-by: itsmattkc itsmattkc@gmail.com

• Clarified CMake option for Win32 unicode

Signed-off-by: itsmattkc 34096995+itsmattkc@users.noreply.github.com

• minor improvements

Signed-off-by: itsmattkc 34096995+itsmattkc@users.noreply.github.com

• fix macro in cpu test cmake

Signed-off-by: itsmattkc 34096995+itsmattkc@users.noreply.github.com