Deprecate parameter.__getitem__

[jenshnielsen]

And therefor the ability to sweep a parameter using the syntax
param[0,1.0,10]

• This syntax is confusing since its not really indexing the parameter
• The implementation requires the input to be floats which is not
  pytonic
• It does nothing that cannot be done with param.sweep

Perhaps it makes more sense to add a sweep function taking a parameter

def sweep(parameter: Parameter, slice) -> SweepFixedValues

and also deprecate sweep.

• Add changelog
• The ability to sweep individual values with [val1,val2, ...] is not supported using sweep
• Setting an individual value with [1] is more clunky
• Update qcodes_loop to not make use of this

[codecov]

Codecov Report

Merging #5036 (5b7faca) into master (069f68d) will decrease coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #5036      +/-   ##
==========================================
- Coverage   67.31%   67.27%   -0.04%     
==========================================
  Files         357      357              
  Lines       29839    29841       +2     
==========================================
- Hits        20085    20077       -8     
- Misses       9754     9764      +10     

[jenshnielsen]

This is not a realistic approach since qcodes_loop makes to heavy use of __getitem__ in all its forms.

Suggest to add a class to qcodes loop that takes a parameter as input and exposes__getitem__ and sweep to use in that package