Rename Signal and Model __call__ methods and remove Component.__call__ method.

[francisco-dlp]

Description of the change

Rename the Model and Signal __call__ methods to _get_current_data and remove the unused Component.__call__ method.

While the previous syntax was compact, it was making the code hard to read for those who were not familiar with it.

Progress of the PR

• Change implemented (can be split into several points),
• update docstring (if appropriate),
• update user guide (if appropriate),
• add an changelog entry in the upcoming_changes folder (see upcoming_changes/README.rst),
• Check formatting changelog entry in the readthedocs doc build of this PR (link in github checks)
• add tests,
• ready for review.

[francisco-dlp]

Note that I have branched out from #3202. We must wait until #3202 is merged to merge this.

[codecov]

Codecov Report

Attention: 10 lines in your changes are missing coverage. Please review.

Comparison is base (0df9467) 81.17% compared to head (0da946c) 80.98%.

Additional details and impacted files

@@                  Coverage Diff                   @@
##           RELEASE_next_major    #3238      +/-   ##
======================================================
- Coverage               81.17%   80.98%   -0.20%     
======================================================
  Files                     140      140              
  Lines                   20363    20359       -4     
  Branches                 4819     4819              
======================================================
- Hits                    16530    16488      -42     
- Misses                   2760     2808      +48     
+ Partials                 1073     1063      -10     

Files	Coverage Δ
hyperspy/_components/gaussian.py	97.33% <100.00%> (ø)
hyperspy/_components/lorentzian.py	97.29% <100.00%> (ø)
hyperspy/_components/offset.py	94.33% <100.00%> (ø)
hyperspy/_components/polynomial.py	96.82% <ø> (ø)
hyperspy/_components/skew_normal.py	91.00% <100.00%> (ø)
hyperspy/_signals/complex_signal.py	93.75% <100.00%> (ø)
hyperspy/_signals/signal1d.py	75.09% <100.00%> (ø)
hyperspy/_signals/signal2d.py	88.39% <100.00%> (+6.54%)	⬆️
hyperspy/component.py	90.27% <100.00%> (-0.07%)	⬇️
hyperspy/drawing/markers.py	96.26% <100.00%> (ø)
... and 5 more

... and 2 files with indirect coverage changes

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[ericpre]

The alternative is to make the PR to the exspy branch just need to push the exspy branch to this repo (hyperspy/hyperspy) and change to that branch in this PR.
Anyway I m travelling for the rest of the week and forgot my laptop... 🤦‍♂️ So I will not do anything for the rest of the week.

[ericpre]

It may be worth mentioned explicitly that s() where s being an instance of BaseSignal is removed. Most users will not know that s() is the same as s.__call__.
As this privatise this functionality, it may be worth mentioned it explicitly here?