Change return type of trim functions with char argument to varchar

[ebyhr]

Description

Change return type of trim functions with char argument to varchar

Documentation

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# General
* Fix `trim`, `ltrim` and `rtim` function results when the argument is `char` type. 
  Previously, it returned padded results as `char` type. It returns `varchar` type without padding now. ({issue}`11440`)

[findepi]

Change return type of trim, ltrim and rtim functions with char arguments to varchar.

it's not only about return type.
For example, rtrim(char) was a no-op, the result was always the same as the input, so this fixes the return value as well.