This is a comprehensive refactoring of the error mechanism of the Intl extension.
By moving the prefixing of the current method/function being executed to actual error message creation by accessing the execution context, we get the following benefits:
- Accurate error messages indicating *what* call caused the error
- As we *always* "copy" the message, the `copyMsg` arg becomes unused, meaning we can reduce the size of the `intl_error` struct by 4 bytes.
- Saving it as a zend_string means we know the length of the message
- Remove the need to pass around a "function name" `char*` across multiple calls
- Use Intl's exception mechanism to generate exceptions for constructor call
- This removes the need for replacing the error handler
- Which didn't do anything anyway in silent mode, which required throwing non-descriptive exceptions
