[Feat] - Performance Improvements For TS Files in src/

[adithyaakrishna]

Is your feature request related to a problem? Please describe.

The typescript files in the src/ directory needs performance improvements in terms of code and code readability.

• GLDraw.ts
• GLModel.ts
• GLShape.ts
• GLViewer.ts
• Gradient.ts
• Label.ts
• ProteinSurface4.ts
• VolumeData.ts
• VolumetricRender.ts
• autoload.ts
• colors.ts
• glcartoon.ts
• index.ts
• partialCharges.ts
• specs.ts
• utilities.ts

Describe the solution you'd like
I would like to improve the code base of the 3Dmol.js by using the latest JavaScript methods along with increasing the readability of these files

Note: I have created this issue to track the file improvements with respect to the above files, and each commit/PR will improve the performance aspects of the code along with increasing code readability