Optimize internal calls by passing only stack end for arguments

[chfast]

Instead of passing the reference to the call arguments (a span on the top of the stack) just pass the pointer to the stack end.
Also, don't get the result by ExecutionResult, just expect the result being set to args[0] and the new stack end pointer to be returned.

By this change, the caller does not need to know what the type of the callee function is. See invoke_function() simplification. It only passes the stack pointer and updates the stack pointer after the call.

1. This is a prototype, implementation is messy.
2. The host functions are not updated to the new calling convention. So there is even more execute() wrapping currently. But they may and probably should be updated.
3. I used "stack end", but also "stack top" can be used. The "stack end" looked easier and safer for prototype.
4. Returning nullptr means trap, but this may be a trap for call without arguments where nullptr could be passed as the "no arguments" value. Currently the wrapper handles that nicely (see fake_arg). But we can consider some sentinel address values.
5. It would be better to handle the imported function calls in the wrapper or in call implementation, not in the execute(). I realized this to late to change the design in the prototype.

[codecov]

Codecov Report

Merging #642 (254e779) into skip_nop_instructions (2bdbbc5) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@                  Coverage Diff                   @@
##           skip_nop_instructions     #642   +/-   ##
======================================================
  Coverage                  98.36%   98.37%           
======================================================
  Files                         69       69           
  Lines                       9626     9668   +42     
======================================================
+ Hits                        9469     9511   +42     
  Misses                       157      157           

[axic]

@chfast I think these tests could be merged anyway.

[chfast]

#641.