Add trigger for smarty error event

[mattwire]

See civicrm/civicrm-core#16918

They need to be merged at the same time.

We can't override this function in CRM_Core_Smarty because it actually gets triggered from the Smarty_Compiler class which is not inherited.

Previously smarty errors (such as parse errors) were silently ignored in most cases making debugging templates extremely difficult.

[civibot]

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[seamuslee001]

as per civicrm/civicrm-core#16918 confirmed that this works merging