Escape Simple-ML keywords when used as name

[lars-reimann]

Is your feature request related to a problem? Please describe

Currently the created stubs have a few remaining syntax errors. These are caused by Simple-ML keywords being used as names of API elements. For example, some parameters are called step in sklearn.

Desired solution

It's now possible to use keywords as names by enclosing them in ``, e.g. `step`. Here's the full list of Simple-ML keywords:

• _
• and
• annotation
• as
• attr
• callable
• class
• enum
• false
• fun
• import
• in
• lambda
• not
• null
• or
• out
• package
• static
• step
• sub
• super
• true
• union
• val
• vararg
• where
• workflow
• yield

Additionally, the API elements should be marked with the Simple-ML @PythonName annotation (not to be confused with the annotations of the API editor), which contains the corresponding name in the Python API.

Example

Currently generated:

fun f(step: Any?)

What should be generated, since step is a keyword in Simple-ML:

fun f(@PythonName("step") `step`: Any?)

[lars-reimann]

Won't be needed once #327 is done.