Add Indic Shaper

[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 #216

[codecov[bot]]

Codecov Report

Merging #344 (5f763f5) into main (9b00ed7) will increase coverage by 1%. The diff coverage is 90%.

@@           Coverage Diff           @@
##            main    #344     +/-   ##
=======================================
+ Coverage     85%     86%     +1%     
=======================================
  Files        234     238      +4     
  Lines      13933   15187   +1254     
  Branches    1919    2110    +191     
=======================================
+ Hits       11844   13071   +1227     
+ Misses      1635    1624     -11     
- Partials     454     492     +38     

Flag	Coverage Δ
unittests	86% <90%> (+1%)	:arrow_up:

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

Files Changed	Coverage Δ
src/SixLabors.Fonts/FontMetrics.cs	100% <ø> (ø)
...ts/Unicode/Resources/IndicShapingTrie.Generated.cs	100% <ø> (ø)
src/SixLabors.Fonts/GlyphPositioningCollection.cs	91% <66%> (-1%)	:arrow_down:
...Tables/AdvancedTypographic/Shapers/HangulShaper.cs	84% <78%> (ø)
.../Tables/AdvancedTypographic/Shapers/IndicShaper.cs	78% <78%> (ø)
...les/AdvancedTypographic/Shapers/UniversalShaper.cs	83% <79%> (+1%)	:arrow_up:
...es/AdvancedTypographic/GSub/LookupType4SubTable.cs	90% <83%> (+11%)	:arrow_up:
src/SixLabors.Fonts/TextLayout.cs	85% <83%> (+<1%)	:arrow_up:
...es/AdvancedTypographic/GPos/LookupType3SubTable.cs	61% <87%> (+1%)	:arrow_up:
src/SixLabors.Fonts/GlyphSubstitutionCollection.cs	92% <88%> (+2%)	:arrow_up:
... and 30 more

... and 8 files with indirect coverage changes

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[JimBobSquarePants]

I'm still finishing off porting the tests but I think this is in a position to start reviewing.

[JimBobSquarePants]

OK. Finished!