Revert "BLI: Refactor vector types & functions to use templates"

Reverted because the commit removes a lot of commits.

This reverts commit a2c1c368af.

source/blender/blenlib/BLI_memory_utils.hh

@@ -557,4 +557,13 @@ Container &move_assign_container(Container &dst, Container &&src) noexcept(
   return dst;
 }
 
+/**
+ * Utility macro that wraps `std::enable_if` to make it a bit easier to use and less verbose for
+ * SFINAE in common cases.
+ *
+ * \note Often one has to invoke this macro with double parenthesis. That's because the condition
+ * often contains a comma and angle brackets are not recognized as parenthesis by the preprocessor.
+ */
+#define BLI_ENABLE_IF(condition) typename std::enable_if_t<condition> * = nullptr
+
 }  // namespace blender