ExperimentalBundler: merge bundleBehavior for isolated dependencies

[wbinnssmith]

This:

• Adds a nullable property mainEntryAsset to bundle objects in the ExperimentalBundler for ease of reference
• Combines bundles down to the "lowest common denominator" by overriding bundleBehavior and needsStableName based on other incoming dependencies. This is a breaking change from the current bundler, trading potential asset deduplication for bundle deduplication.

One case we'll need to handle before landing:
* [ ] Marking a bundle as existing both as an inline bundle and a non-inline bundle. Currently we never write inline bundles to disk. In this case we'll need to. Let's defer this, as it seems like different asset bundleBehavior creates different assets, and as far as I can tell, it's not possible to have a non-inline asset and an inline dependency.

Test Plan: Adjusted existing test(s) to use the reduced bundle count

[parcel-benchmark]

Benchmark Results

Kitchen Sink 🚨

Timings

Description	Time	Difference
Cold	FAILED	-0.00ms
Cached	FAILED	-0.00ms

Cold Bundles

No bundles found, this is probably a failed build...

Cached Bundles

No bundles found, this is probably a failed build...

React HackerNews ✅

Timings

Description	Time	Difference
Cold	9.15s	+19.00ms
Cached	441.00ms	+4.00ms

Cold Bundles

No bundle changes detected.

Cached Bundles

No bundle changes detected.

AtlasKit Editor ✅

Timings

Description	Time	Difference
Cold	1.58m	-964.00ms
Cached	2.58s	+4.00ms

Cold Bundles

No bundle changes detected.

Cached Bundles

Bundle	Size	Difference	Time	Difference
dist/esm.6190c9ac.js	61.54kb	+0.00b	39.21s	-33.05s 🚀
dist/index.html	240.00b	+0.00b	35.47s	-36.82s 🚀

Three.js ✅

Timings

Description	Time	Difference
Cold	6.58s	+34.00ms
Cached	268.00ms	-10.00ms

Cold Bundles

No bundle changes detected.

Cached Bundles

No bundle changes detected.

Click here to view a detailed benchmark overview.

[devongovett]

different asset bundleBehavior creates different assets

I think asset.bundleBehavior but not dependency.bundleBehavior?

parcel/packages/core/core/src/Dependency.js

Lines 44 to 53 in e51955f

	let id =
	opts.id ||
	hashString(
	(opts.sourceAssetId ?? '') +
	opts.specifier +
	opts.env.id +
	(opts.target ? JSON.stringify(opts.target) : '') +
	(opts.pipeline ?? '') +
	opts.specifierType +
	(opts.priority ?? 'sync'),

[101arrowz]

This is probably a blocker for #8000; probably best to decide how exactly duplicate assets with different bundleBehavior should be bundled before deciding whether to merge generated dependencies or not.

[devongovett]

Is this still needed @wbinnssmith @AGawrys?

[devongovett]

This was merged as part of another PR.