Fixes bugs related to unicode support in polynomial-hash functions

[dubzzz]

Details:

This Pull Request fixes bugs related to unicode support in polynomial-hash functions:

• Method charToNumber of PolynomialHash was wrongly computed the code point value of a character: codePointAt is already aware of surrogate pairs (which is not the case of charCodeAt)
• Method roll of PolynomialHash ignored unicode characters totally
• SimplePolynomialHash was not aware of unicode

How did I find it?

Originally I wanted to check how I could rewrite the existing for-loop based tests into something based on property based. Then it clearly appeared that the test can be simplified given the switch to property based: roll(hash(XYZ), XYZ, YZA) === hash(YZA) whatever the values of X, Y, Z, A.

The final version of the test can be read as follow:
For any A single character, B single character and W string,
roll(hash(A + W), A + W, W + B) === hash(W + B)

As a side note, I strongly believe that adding such kind of tests would highly help to detect such bugs easily. Up to now it has detected the following: #100, #101, #102, #110 and #129.

And also #305, #306, #307, #308.

[codecov]

Codecov Report

Merging #304 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #304   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files         147    147           
  Lines        2591   2588    -3     
  Branches      432    431    -1     
=====================================
- Hits         2591   2588    -3

Impacted Files	Coverage Δ
...yptography/polynomial-hash/SimplePolynomialHash.js	100% <100%> (ø)	⬆️
...hms/cryptography/polynomial-hash/PolynomialHash.js	100% <100%> (ø)	⬆️

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[dubzzz]

@trekhleb Any updates? I can rebase the branch if needed