Support create/drop global function.
When you create a custom function, it can only be used within in one database. It cannot be used in other database/catalog. When there are many databases/catalog, it needs to create function one by one.
## Problem summary
Describe your changes.
1、 When a function is created or deleted, add the global keyword.
CREATE [GLOBAL] [AGGREGATE] [ALIAS] FUNCTION function_name (arg_type [, ...]) [RETURNS ret_type] [INTERMEDIATE inter_type] [WITH PARAMETER(param [,...]) AS origin_function] [PROPERTIES ("key" = "value" [, ...]) ]
DROP [GLOBAL] FUNCTION function_name (arg_type [, ...])
2、A completely global global function is set, and the global function metadata is stored in the image. The function lookup strategy is to look in the database first, and if it can't be found, it looks in the global function.
Co-authored-by: lexluo <lexluo@tencent.com>
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