text: Title: Add public argument conversion API for libraries and other tools
  Body: Hi @pekkaklarck ,
  
  We are using `TypeConverter` class in Robot Framework Browser in multiple places, to convert arguments of `*varagrs` when calling internal keywords.
  Unfortunately this API is no longer be able to digest real `type` values.
  
  ```python
  from robot.running.arguments.typeconverters import TypeConverter
  TypeConverter.converter_for(int)
  ```
  
  We need “dynamic” type conversion because of many reasons.
  
  With dynamic i mean we do Robot type conversion inside Browser lib when Robot is not able to do.
  
  1. We do have situations where we deprecate positional args in favour of named only ones. In these cases we introduce a `*varags` argument that collects all old positional args and assigns them in the old order to the variables inside. Therefore there is no type hinting in the arguments. but we have a Catalog of the original types which can be used to convert.
  2. We do have keywords like `Promise To` and `Wait For Condition` which calls our keywords internally and has `*args` to take the arguments. These two keywords iterate over the called keywords interface and try to convert the arguments according to their type. Also in this case we want/need to support dynamic argument conversion.
  
  For us it is not really important, if exactly this function `converter_for()` will stay compatible or if a new function will be implemented to get to get the proper converter for a Python type.
  However it would be more convenient for our users to stay compatible, so they do not necessarily need to update Browser, when updating RF.
  
  We do currently:
  ```python
  converter = TypeConverter.converter_for(argument_type)
                  if converter is not None:
                      params[argument_name] = converter.convert(
                          argument_name, params.get(argument_name)
                      )
  ```
  
  A Public API for this would be nice too.
  Or maybe even just a convenient function for Converting value to type as a static method.
  Something like `TypeConverters.convert_to_type(name: str, value: Any, destination_type: type)` 
  
  Cheers