Refactor getMathMLEntity() to use std::string_view and OUString for string handling, so that there is less string conversion when calling this function. Use std::find_if to find formula in array instead of a loop. Change-Id: I0ed98d33e62f6bc730ac750f4fd545d2f07145fc Reviewed-on: https://gerrit.libreoffice.org/c/core/+/182065 Tested-by: Jenkins Reviewed-by: Hossein <hossein@libreoffice.org>