fix(oiiotool): Use normalized path when creating wildcard path pattern (AcademySoftwareFoundation#4904)

On Windows, using a wildcard input path containing `\` back slashes
would lead to failures because it would be compared with file paths
containing `/` forward slashes. Use the existing
`Filesystem::generic_filepath` API (which calls `path::generic_string`)
to get a normalized path containing consistent directory separators.

An example of the existing failure:
```
.\oiiotool.exe -v t:\render\foo_#.png --resize 160x90 -o t:\smaller_#.png

oiiotool WARNING : No frame number or views matched the wildcards
oiiotool ERROR: read : File does not exist: "t:\render\foo_#.png"
Full command line was:
> oiiotool.exe -v t:\\render\\foo_#.png --resize 160x90 -o t:\\smaller_#.png
```
Workaround - without this PR you would have to use an input path
containing `/`:
```
.\oiiotool.exe -v t:/render/foo_#.png --resize 160x90 -o t:\smaller_#.png
Reading t:/render/foo_0001.png
Writing t:\smaller_0001.png
Reading t:/render/foo_0002.png
Writing t:\smaller_0002.png
```

Signed-off-by: Jesse Yurkovich <jesse.y@gmail.com>

Author: jessey-git

src/libutil/filesystem.cpp

@@ -911,7 +911,7 @@ Filesystem::parse_pattern(const char* pattern_, int framepadding_override,
 
     // std::cout << "Format: '" << fmt << "'\n";
 
-    normalized_pattern = prefix + fmt + suffix;
+    normalized_pattern = Filesystem::generic_filepath(prefix + fmt + suffix);
     framespec          = thesequence;
 
     return true;