Replaced concat with push for better performance per #682

[Balearica]

Description

Replaces instances of d = d.concat(...) with push within cmap functions for improved performance per #682. Should not impact results. Conceptually speaking, this is almost identical to #513.

Additionally, t.segments.sort was being run every time a new element was added within a loop; I edited to only run once after all elements are inserted.

Motivation and Context

See #682. In short, the performance of font.toArrayBuffer() can be poor, including >30+ second runtimes for certain large fonts. This PR fixes that.

On my system (Chrome, Windows 10), this PR reduces the runtime for writing NotoSansSC from 36 seconds to 8 seconds (78% reduction), and reduces the runtime for NotoSerifSC from 33 seconds to 8 seconds (76% reduction).

How Has This Been Tested?

The unit tests pass and I am using a version with these changes in my project. Additionally, the change is conceptually simple and narrow in scope.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I did npm run test and all tests passed green (including code styling checks).
• I have added tests to cover my changes.
• My change requires a change to the documentation.
• I have updated the README accordingly.
• I have read the CONTRIBUTING document.

[Connum]

Could you add a performance test by measuring the time it takes to run toArrayBuffer() and making sure it's below a certain threshold that it was above without the change?

[Connum]

I will add a test and a new local rule for banning concat(). But I can clearly confirm the performance improvement! I'll review and merge this soon.

[Connum]

Looking good!