Properly support custom 500 page in the web server

[shuding]

In the web runtime, currently we use absolute500Path || absoluteErrorPath to act like /_error. This PR fixes the behavior to use the /pages/500.js for 500 errors and /pages/_error.js for 500 fallback and other errors.

Bug

• Related issues linked using fixes #number
• Integration tests added
• Errors have helpful link attached, see contributing.md

Feature

• Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
• Related issues linked using fixes #number
• Integration tests added
• Documentation added
• Telemetry added. In case of a feature if it's used or not.
• Errors have helpful link attached, see contributing.md

Documentation / Examples

• Make sure the linting passes by running yarn lint

[ijjk]

Stats from current PR

Default Build (Increase detected ⚠️)

General Overall increase ⚠️

	vercel/next.js canary	shuding/next.js shu/f8bc	Change
buildDuration	11.5s	10.9s	-540ms
buildDurationCached	3s	3s	-29ms
nodeModulesSize	358 MB	358 MB	⚠️ +1.33 kB

Page Load Tests Overall increase ✓

	vercel/next.js canary	shuding/next.js shu/f8bc	Change
/ failed reqs	0	0	✓
/ total time (seconds)	2.734	2.598	-0.14
/ avg req/sec	914.33	962.18	+47.85
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.323	1.21	-0.11
/error-in-render avg req/sec	1890.13	2066.16	+176.03

Client Bundles (main, webpack, commons)

	vercel/next.js canary	shuding/next.js shu/f8bc	Change
450.HASH.js gzip	179 B	179 B	✓
framework-HASH.js gzip	42.2 kB	42.2 kB	✓
main-HASH.js gzip	27.2 kB	27.2 kB	✓
webpack-HASH.js gzip	1.44 kB	1.44 kB	✓
Overall change	71 kB	71 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	shuding/next.js shu/f8bc	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	shuding/next.js shu/f8bc	Change
_app-HASH.js gzip	1.37 kB	1.37 kB	✓
_error-HASH.js gzip	194 B	194 B	✓
amp-HASH.js gzip	312 B	312 B	✓
css-HASH.js gzip	326 B	326 B	✓
dynamic-HASH.js gzip	2.37 kB	2.37 kB	✓
head-HASH.js gzip	350 B	350 B	✓
hooks-HASH.js gzip	919 B	919 B	✓
image-HASH.js gzip	4.94 kB	4.94 kB	✓
index-HASH.js gzip	263 B	263 B	✓
link-HASH.js gzip	2.19 kB	2.19 kB	✓
routerDirect..HASH.js gzip	321 B	321 B	✓
script-HASH.js gzip	383 B	383 B	✓
withRouter-HASH.js gzip	318 B	318 B	✓
85e02e95b279..7e3.css gzip	107 B	107 B	✓
Overall change	14.4 kB	14.4 kB	✓

Client Build Manifests

	vercel/next.js canary	shuding/next.js shu/f8bc	Change
_buildManifest.js gzip	460 B	460 B	✓
Overall change	460 B	460 B	✓

Rendered Page Sizes

	vercel/next.js canary	shuding/next.js shu/f8bc	Change
index.html gzip	531 B	531 B	✓
link.html gzip	545 B	545 B	✓
withRouter.html gzip	526 B	526 B	✓
Overall change	1.6 kB	1.6 kB	✓

---

Default Build with SWC (Decrease detected ✓)

General Overall increase ⚠️

	vercel/next.js canary	shuding/next.js shu/f8bc	Change
buildDuration	14.1s	15.5s	⚠️ +1.4s
buildDurationCached	3s	2.9s	-26ms
nodeModulesSize	358 MB	358 MB	⚠️ +1.33 kB

Page Load Tests Overall decrease ⚠️

	vercel/next.js canary	shuding/next.js shu/f8bc	Change
/ failed reqs	0	0	✓
/ total time (seconds)	2.565	2.604	⚠️ +0.04
/ avg req/sec	974.56	960.25	⚠️ -14.31
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.211	1.228	⚠️ +0.02
/error-in-render avg req/sec	2065.08	2035.36	⚠️ -29.72

Client Bundles (main, webpack, commons)

	vercel/next.js canary	shuding/next.js shu/f8bc	Change
450.HASH.js gzip	179 B	179 B	✓
framework-HASH.js gzip	42.3 kB	42.3 kB	✓
main-HASH.js gzip	27.3 kB	27.3 kB	✓
webpack-HASH.js gzip	1.44 kB	1.44 kB	✓
Overall change	71.3 kB	71.3 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	shuding/next.js shu/f8bc	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	shuding/next.js shu/f8bc	Change
_app-HASH.js gzip	1.35 kB	1.35 kB	✓
_error-HASH.js gzip	180 B	180 B	✓
amp-HASH.js gzip	305 B	305 B	✓
css-HASH.js gzip	321 B	321 B	✓
dynamic-HASH.js gzip	2.36 kB	2.36 kB	✓
head-HASH.js gzip	342 B	342 B	✓
hooks-HASH.js gzip	911 B	911 B	✓
image-HASH.js gzip	4.97 kB	4.97 kB	✓
index-HASH.js gzip	256 B	256 B	✓
link-HASH.js gzip	2.21 kB	2.21 kB	✓
routerDirect..HASH.js gzip	314 B	314 B	✓
script-HASH.js gzip	375 B	375 B	✓
withRouter-HASH.js gzip	309 B	309 B	✓
85e02e95b279..7e3.css gzip	107 B	107 B	✓
Overall change	14.3 kB	14.3 kB	✓

Client Build Manifests

	vercel/next.js canary	shuding/next.js shu/f8bc	Change
_buildManifest.js gzip	459 B	459 B	✓
Overall change	459 B	459 B	✓

Rendered Page Sizes

	vercel/next.js canary	shuding/next.js shu/f8bc	Change
index.html gzip	531 B	531 B	✓
link.html gzip	545 B	545 B	✓
withRouter.html gzip	526 B	526 B	✓
Overall change	1.6 kB	1.6 kB	✓

Commit: 90bd8d7