ext/intl: Refactor error handling

[Girgias]

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

[devnexen]

I appreciate the heap allocations savings ; I ll have a better look later this week. Are you still working on it though (W.I.P) ?

[Girgias]

I appreciate the heap allocations savings ; I ll have a better look later this week. Are you still working on it though (W.I.P) ?

Forgot to update the title of the PR, but I think I'm done modifying the C/C++ code, might work on the tests to get rid of the usage of warnings as the intl.error_level INI deprecation looks likely to pass so that it doesn't end up with a bunch of deprecations :)