More explicit typing for IncrementalCache API

[devknoll]

Make the typing for IncrementalCache more explicit. With streaming, we’ll want to stream page data as well as HTML. This is a bit complicated now because we’re overloading pageData for both redirects and pages.

This PR makes the different types explicit. With streaming, the data for redirects is synchronously available, while the data for pages will become a stream.

A follow up PR will add a “stream through” cache in front of IncrementalCache

[ijjk]

Stats from current PR

Default Build (Increase detected ⚠️)

General Overall increase ⚠️

	vercel/next.js canary	azukaru/next.js x-clean-up-incremental-cache	Change
buildDuration	13.9s	14s	⚠️ +163ms
buildDurationCached	3.4s	3.3s	-74ms
nodeModulesSize	49.3 MB	49.3 MB	⚠️ +1.67 kB

Page Load Tests Overall increase ✓

	vercel/next.js canary	azukaru/next.js x-clean-up-incremental-cache	Change
/ failed reqs	0	0	✓
/ total time (seconds)	2.474	2.453	-0.02
/ avg req/sec	1010.61	1019.13	+8.52
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.391	1.375	-0.02
/error-in-render avg req/sec	1797.75	1818.34	+20.59

Client Bundles (main, webpack, commons)

	vercel/next.js canary	azukaru/next.js x-clean-up-incremental-cache	Change
359.HASH.js gzip	3.09 kB	3.09 kB	✓
framework-HASH.js gzip	42 kB	42 kB	✓
main-HASH.js gzip	20.6 kB	20.6 kB	✓
webpack-HASH.js gzip	1.49 kB	1.49 kB	✓
Overall change	67.2 kB	67.2 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	azukaru/next.js x-clean-up-incremental-cache	Change
polyfills-HASH.js gzip	31.1 kB	31.1 kB	✓
Overall change	31.1 kB	31.1 kB	✓

Client Pages

	vercel/next.js canary	azukaru/next.js x-clean-up-incremental-cache	Change
_app-HASH.js gzip	803 B	803 B	✓
_error-HASH.js gzip	3.18 kB	3.18 kB	✓
amp-HASH.js gzip	526 B	526 B	✓
css-HASH.js gzip	329 B	329 B	✓
hooks-HASH.js gzip	903 B	903 B	✓
index-HASH.js gzip	263 B	263 B	✓
link-HASH.js gzip	1.65 kB	1.65 kB	✓
routerDirect..HASH.js gzip	322 B	322 B	✓
withRouter-HASH.js gzip	320 B	320 B	✓
bb14e60e810b..30f.css gzip	125 B	125 B	✓
Overall change	8.42 kB	8.42 kB	✓

Client Build Manifests

	vercel/next.js canary	azukaru/next.js x-clean-up-incremental-cache	Change
_buildManifest.js gzip	390 B	390 B	✓
Overall change	390 B	390 B	✓

Rendered Page Sizes

	vercel/next.js canary	azukaru/next.js x-clean-up-incremental-cache	Change
index.html gzip	523 B	523 B	✓
link.html gzip	537 B	537 B	✓
withRouter.html gzip	515 B	515 B	✓
Overall change	1.57 kB	1.57 kB	✓

---

Webpack 4 Mode (Increase detected ⚠️)

General Overall increase ⚠️

	vercel/next.js canary	azukaru/next.js x-clean-up-incremental-cache	Change
buildDuration	12.3s	12.5s	⚠️ +175ms
buildDurationCached	5s	4.8s	-161ms
nodeModulesSize	49.3 MB	49.3 MB	⚠️ +1.67 kB

Page Load Tests Overall increase ✓

	vercel/next.js canary	azukaru/next.js x-clean-up-incremental-cache	Change
/ failed reqs	0	0	✓
/ total time (seconds)	2.455	2.461	⚠️ +0.01
/ avg req/sec	1018.38	1015.89	⚠️ -2.49
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.404	1.364	-0.04
/error-in-render avg req/sec	1780	1833.24	+53.24

Client Bundles (main, webpack, commons)

	vercel/next.js canary	azukaru/next.js x-clean-up-incremental-cache	Change
14.HASH.js gzip	3.11 kB	3.11 kB	✓
677f882d2ed8..HASH.js gzip	13.9 kB	13.9 kB	✓
framework.HASH.js gzip	41.8 kB	41.8 kB	✓
main-HASH.js gzip	7.81 kB	7.81 kB	✓
webpack-HASH.js gzip	1.19 kB	1.19 kB	✓
Overall change	67.8 kB	67.8 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	azukaru/next.js x-clean-up-incremental-cache	Change
polyfills-HASH.js gzip	31.3 kB	31.3 kB	✓
Overall change	31.3 kB	31.3 kB	✓

Client Pages

	vercel/next.js canary	azukaru/next.js x-clean-up-incremental-cache	Change
_app-HASH.js gzip	791 B	791 B	✓
_error-HASH.js gzip	3.83 kB	3.83 kB	✓
amp-HASH.js gzip	531 B	531 B	✓
css-HASH.js gzip	333 B	333 B	✓
hooks-HASH.js gzip	910 B	910 B	✓
index-HASH.js gzip	227 B	227 B	✓
link-HASH.js gzip	1.64 kB	1.64 kB	✓
routerDirect..HASH.js gzip	295 B	295 B	✓
withRouter-HASH.js gzip	292 B	292 B	✓
e025d2764813..52f.css gzip	125 B	125 B	✓
Overall change	8.98 kB	8.98 kB	✓

Client Build Manifests

	vercel/next.js canary	azukaru/next.js x-clean-up-incremental-cache	Change
_buildManifest.js gzip	418 B	418 B	✓
Overall change	418 B	418 B	✓

Rendered Page Sizes

	vercel/next.js canary	azukaru/next.js x-clean-up-incremental-cache	Change
index.html gzip	569 B	569 B	✓
link.html gzip	581 B	581 B	✓
withRouter.html gzip	561 B	561 B	✓
Overall change	1.71 kB	1.71 kB	✓

Commit: 23c3236