Fix rendering along open paths.

[JimBobSquarePants]

Prerequisites

• [x] I have written a descriptive pull-request title
• [x] I have verified that there are no overlapping pull-requests open
• [x] I have verified that I am following matches the existing coding patterns and practice as demonstrated in the repository. These follow strict Stylecop rules :cop:.
• [x] I have provided test coverage for my change (where applicable)

Description

Fixes #234

The issue is caused by our code which calculates the position of a point along the given path at a given distance. The code works well for closed paths since it reduces the distance to the remainder (distance %= path.Length) which makes a nice loop.

For open paths we don't want to do that, we want to create a new virtual point at the correct angle and distance calculated from the last two points in the path.

I've also renamed DrawLines to DrawLine as you can only draw one line at a time using the method.

[codecov[bot]]

Codecov Report

Merging #263 (41174d1) into main (cee21d9) will increase coverage by 0%. The diff coverage is 80%.

@@         Coverage Diff         @@
##           main   #263   +/-   ##
===================================
  Coverage    61%    61%           
===================================
  Files       100    100           
  Lines      6449   6427   -22     
  Branches   1378   1374    -4     
===================================
- Hits       3934   3923   -11     
+ Misses     2314   2308    -6     
+ Partials    201    196    -5     

Flag	Coverage Δ
unittests	61% <80%> (+<1%)	:arrow_up:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/ImageSharp.Drawing/Shapes/ComplexPolygon.cs	76% <0%> (-3%)	:arrow_down:
...mageSharp.Drawing/Shapes/PolygonClipper/Clipper.cs	73% <0%> (ø)
...rawing/Processing/Extensions/DrawLineExtensions.cs	100% <100%> (ø)
...rocessing/Processors/Text/RichTextGlyphRenderer.cs	95% <100%> (+1%)	:arrow_up:
src/ImageSharp.Drawing/Shapes/InternalPath.cs	90% <100%> (+2%)	:arrow_up:
...ImageSharp.Drawing/Shapes/Text/PathGlyphBuilder.cs	75% <100%> (+9%)	:arrow_up:
src/ImageSharp.Drawing/Shapes/Text/TextBuilder.cs	62% <100%> (ø)

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[JimBobSquarePants]

Would it be possible to get some eyes on this?