Lazy wrapper instantiation

[pmdartus]

Changes

This PR is an early draft for lazy wrapper instantiation. Instead of eagerly create a wrapper for each new impl, the wrapper is only created when accessed by userland code.

While the results are REALLY encouraging, there are still a couple of test failures in jsdom (mainly related to events). Running this change against jsdom performance benchmark we can measure a 44% reduction in memory consumption and a 20% to 200% performance improvement across all the tests. More details in the results section.

Fixes #157

Results

Memory

Memory (MB)	p50	p75	p90	p95
Baseline	1328.97	1560.35	1669.04	1726.82
Lazy	922.80	1126.09	1315.43	1392.72
Delta	-44.01%	-38.56%	-26.88%	-23.99%

Benchmark Performance

Benchmark	Baseline (ops/sec)	Lazy wrapper (ops/sec)	Detla
dom/compare-document-position/compare ancestor	18,986.00	18,440	2.88%
dom/compare-document-position/compare descendant	18,110.00	19,403	-7.14%
dom/compare-document-position/compare siblings	1,107,701.00	1,120,706	-1.17%
dom/construction/createComment	1,276,052.00	2,263,382	-77.37%
dom/construction/createDocumentFragment	1,410,648.00	2,188,373	-55.13%
dom/construction/createElement	192,790.00	646,840	-235.52%
dom/construction/createEvent	215,484.00	209,256	2.89%
dom/construction/createNodeIterator	1,217,542.00	1,747,421	-43.52%
dom/construction/createProcessingInstruction	540,648.00	903,657	-67.14%
dom/construction/createTextNode	991,920.00	1,732,976	-74.71%
dom/inner-html/tables	0.31	0.39	-25.81%
dom/named-properties/setAttribute(): Remove a named property from window	3,049.00	3,591	-17.78%
dom/tree-modification/appendChild: many parents	22.03	22.69	-3.00%
dom/tree-modification/appendChild: many siblings	240,373.00	298,791	-24.30%
dom/tree-modification/appendChild: no siblings	234,210.00	262,268	-11.98%
dom/tree-modification/insertBefore: many siblings	208,446.00	264,970	-27.12%
dom/tree-modification/removeChild: many parents	116.00	130	-12.07%
dom/tree-modification/removeChild: many siblings	116,963.00	133,050	-13.75%
dom/tree-modification/removeChild: no siblings	111,543.00	129,702	-16.28%
html/parsing/text	13.10	13.88	-5.95%
jsdom/api/new JSDOM() defaults	240.00	256	-6.67%
jsdom/api/new JSDOM() with many elements	26.51	33.57	-26.63%

[domenic]

Amazing!!

Would you be able to remove the impl -> implSymbol renaming for now, or maybe do it as a separate commit? That would make review much easier (including of the generated code).

[pmdartus]

Yes, I will do that soon. I was just too excited to share those numbers.

[ExE-Boss]

Why not use a getter that turns into a data property?

That will remove the need for createWrapperSymbol and globalObjectSymbol.