Enable floating point ranges

[mvd4]

Description

The generator helper range(start, end, step) currently only supports integer ranges.
This seems to be an artificial limitation, as the underlying RangeGenerator<T> works fine also for floating point types.

This PR changes the static_assert that limits the types for range(start, end, step) to also support floating point types. It also introduces additional tests to cover the extended functionality.

[codecov]

Codecov Report

Merging #1776 into master will decrease coverage by 2.11%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1776      +/-   ##
==========================================
- Coverage   87.97%   85.86%   -2.11%     
==========================================
  Files         138      131       -7     
  Lines        5468     3754    -1714     
==========================================
- Hits         4810     3223    -1587     
+ Misses        658      531     -127

[horenmar]

Actually it does not support floating point numbers intentionally. The original PR had no limits on the generator, but I wanted to avoid bug reports from people who'd use the generator for floating point numbers, without taking proper care of edge conditions caused by floating point rounding.

This is incidentally also why the static assert is placed in the helper function and not in the generator class itself -- it allows advanced users to create the generator manually if needed.

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I'll think about lifting the restriction.