Add strict equality operator to TS files src/*

[prajwalkulkarni]

💫 Changelog

⭐ Updates TS files src/* to use strict equality operator.
⭐ Only those conditions are updated where it is safe to update == to === and != to !==. (E.g: statements where types of both the operands are known and same, operands that use typeof etc.)
⭐ There still exist several statements where the operator is not updated as the logic might change (== returns true on comparing null and undefined whereas === returns false) or the types of operands are not known (any). Updating this requires manual efforts and it'll be easier once the type safety of the library has been improved.
⭐ The operators still need to be updated in these paths: src/parsers, src/WebGL which will be done on a separate PR (because it'll be difficult to self-review large file changes before submitting PR)

[codecov]

Codecov Report

Attention: 78 lines in your changes are missing coverage. Please review.

Comparison is base (8c3e9d4) 82.62% compared to head (e5ebc6a) 82.58%.

Files	Patch %	Lines
src/GLViewer.ts	50.00%	15 Missing and 9 partials ⚠️
src/GLModel.ts	66.66%	13 Missing and 3 partials ⚠️
src/utilities.ts	48.14%	3 Missing and 11 partials ⚠️
src/VolumeData.ts	0.00%	2 Missing and 5 partials ⚠️
src/GLShape.ts	66.66%	4 Missing and 1 partial ⚠️
src/autoload.ts	42.85%	4 Missing ⚠️
src/GLDraw.ts	33.33%	2 Missing ⚠️
src/Gradient.ts	81.81%	2 Missing ⚠️
src/VolumetricRender.ts	0.00%	2 Missing ⚠️
src/Label.ts	83.33%	0 Missing and 1 partial ⚠️
... and 1 more

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #754      +/-   ##
==========================================
- Coverage   82.62%   82.58%   -0.04%     
==========================================
  Files         141      141              
  Lines       11496    11493       -3     
  Branches     2126     2126              
==========================================
- Hits         9498     9492       -6     
+ Misses       1667     1665       -2     
- Partials      331      336       +5     

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[prajwalkulkarni]

@dkoes Could you kindly review and let me know if there are any other changes to be made?

cc @NicolasCARPi

[prajwalkulkarni]

UPDATE: Removed typeof wherever a variable/property was compared to "undefined". Added optional chaining wherever a nested property was compared to undefined, e.g.: a.properties[prop] in GLModel.ts where properties is an optional type and could possibly be undefined.