feat(web): add .codepointLength field for SearchQuotientNode types 🚂

[jahorton]

In order to move the implementation of .split operations onto the SearchQuotientNode types, its instances will need a way to recursively find the correct split point. .codepointLength, along with the helper .leftDeleteLength and .insertLength properties, will provide a clear and clean way to do exactly that.

Build-bot: skip build:web
Test-bot: skip

[keymanapp-test-bot]

User Test Results

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User tests are not required

Test Artifacts

• Web
  • KeymanWeb Test Home - build : all tests passed (no artifacts on BuildLevel "build")

[darcywong00]

Shouldn't we set this outside of get()?

[jahorton]

OK, so this gets a bit complicated because of the TS type system.

Note the .insertLength and .leftDeleteLength properties.

Those two properties cannot be set in the SearchQuotientSpur constructor and are thus unavailable for use in initializing the field during construction time. As a result, I opted to take a "lazy initialization" strategy - we'll calculate it once, when it's needed, and lock in the value at that time.

While it could be dynamically generated at runtime on each access, bypassing the need to set an instance field entirely, that'd make accesses an O(N) call each time on the length of the string, rather than O(1). (I'm aiming to optimize the number of KMWString calls, as the code involves lots of branches and loops, thus could suffer significant branch-prediction misses.)

[mcdurdin]

Suggested change

	this._codepointLength = this.parentNode.codepointLength + this.insertLength - this.leftDeleteLength;
	// caching result for performance
	// note that readonly abstract props cannot be accessed in constructor
	this._codepointLength = this.parentNode.codepointLength + this.insertLength - this.leftDeleteLength;

But this does feel a little bit like working too hard for structural elegance (readonly abstract properties) and shooting yourself in the foot in the process because then you need this pattern. Another way of solving this could be by including the value or values as parameters to the SearchQuotientSpur constructor.

[darcywong00]

For maintainability of what bestExample() is calculating, can we we split this change to a const above? (to a descriptive variable) along with some comments how it's "best".