javascript.lang (and family): Various updates

Jeffery To requested to merge jefferyto/gtksourceview:js-updates into master

This is a series of updates mainly for JavaScript (import.meta, String.prototype.replaceAll) and TypeScript (up to TypeScript 3.9). I had to refactor/redo some things, mainly highlighting for object literal and class bodies, in order to accommodate these changes. (I suppose I didn't have to refactor; the previous code worked but it wasn't great.)

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