Path util: BLI_path_contains() case-insensitive on Windows

Make `BLI_path_contains()` case-insensitive on Windows. This behaviour
is dependent on the platform Blender is running on, like the rest of
BLI_path, and not on the style of paths (Windows-style paths will be
treated case-sensitively when Blender is running on Linux/macOS).

source/blender/blenlib/intern/path_util.c

@@ -1951,6 +1951,11 @@ bool BLI_path_contains(const char *container_path, const char *containee_path)
   BLI_path_normalize(NULL, container_native);
   BLI_path_normalize(NULL, containee_native);
 
+#ifdef WIN32
+  BLI_str_tolower_ascii(container_native, PATH_MAX);
+  BLI_str_tolower_ascii(containee_native, PATH_MAX);
+#endif
+
   if (STREQ(container_native, containee_native)) {
     /* The paths are equal, they contain each other. */
     return true;

source/blender/blenlib/tests/BLI_path_util_test.cc

@@ -678,3 +678,11 @@ TEST(path_util, PathContains)
   EXPECT_FALSE(BLI_path_contains("/some/path", "./contents"))
       << "Relative paths are not supported";
 }
+
+#ifdef WIN32
+TEST(path_util, PathContains_Windows_case_insensitive)
+{
+  EXPECT_TRUE(BLI_path_contains("C:\\some\\path", "c:\\SOME\\path\\inside"))
+      << "On Windows path comparison should ignore case";
+}
+#endif