Add lineJoinType and miterLimit parameters to LineChartDataSet (fixes #2180 )

[anton-filimonov]

let users fix sharp edges the way they want, keeping default behaviour same as current.

Issue Link 🔗

#2180

Implementation Details 🚧

There is another PR that is made to solve same issue but it changes the default behaviour and actually also breaks line joins when lineCapType is not .round. This PR is another way to solve that problem, but it also not ideal - multicolored line will not use introduced lineJoinType property because of tricky way to draw that line (actually that tricky way leads to bad line when lineCapType is not .round)

[codecov-io]

Codecov Report

Merging #3797 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #3797      +/-   ##
==========================================
+ Coverage   32.67%   32.69%   +0.01%     
==========================================
  Files         114      114              
  Lines       10754    10757       +3     
==========================================
+ Hits         3514     3517       +3     
  Misses       7240     7240

Impacted Files	Coverage Δ
...ta/Implementations/Standard/LineChartDataSet.swift	30% <ø> (ø)	⬆️
Source/Charts/Renderers/LineChartRenderer.swift	61.81% <100%> (+0.16%)	⬆️

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[liuxuan30]

eh, is this PR exclusive to #3764? meaning we should only merge one of the two?

[anton-filimonov]

@liuxuan30 yes. Another one breaks line joins for single color line (for multicolored line it was broken long ago), so we have to choose only one of them

[liuxuan30]

OK. Let's discuss in #3764 then to find a proper one.