This pull request converts Next.js' export CLI command to use TypeScript. This is useful for upcoming changes.

* Add new `srcRoute` attribute to SprRoute

* Update prerender manfiest test snapshot

* Fix types

* Update Prerender Manifest

* Fix typescript

* Add SPR Dynamic Routes to Manifest
This adds dynamic routes for SPR pages to the prerender manifest so we can configure the Now Builder to handle these routes as SPR routes. Otherwise, they're treated like normal `getInitialProps` pages.

* Fix types

* Configure the Default Revalidate
The default revalidate behavior should be configured by Next.js. Otherwise, the behavior might drift or change in non-semver compliant ways between Next.js and the builder (or other 3rd party setups).

* Add additional comment

Per the HTTP specification, only natural numbers may be used for caching durations. We should enforce this with a really helpful error message.

The Now CDN does not support the `stale-if-error` header and already behaves like that for `stale-while-revalidate`.

Removing this header allows Now CDN to use its default headers instead of sending _only_ `stale-if-error` after stripping `s-maxage` and `stale-while-revalidate`.

* Add revalidate header and error when invalid
object from getStaticProps

* Make sprCache no-op in dev mode

* Update packages/next/next-server/server/next-server.ts

* Update tests for fixes

* Update getStaticProps error and add test

* Update manifest test

* Add validating revalidate value

* Apply suggestions from code review
Co-Authored-By: NJoe Haddad <joe.haddad@zeit.co>

* Change from error to warning high revalidate value

* Add find-pages-dir

* Add support for src directory

* Add test for pages dir preference

* Update comment

* initial commit for SPRv2

* Add initial SPR cache handling

* update SPR handling

* Implement SPR handling in render

* Update tests, handle caching with serverless next
start, add TODOs, and update manifest generating

* Handle no prerender-manifest from not being used

* Fix url.parse error

* Apply suggestions from code review
Co-Authored-By: NJoe Haddad <joe.haddad@zeit.co>

* Replace set with constants in next-page-config

* simplify sprStatus.used

* Add error if getStaticProps is used with getInitialProps

* Remove stale TODO

* Update revalidate values in SPR cache for non-seeded routes

* Apply suggestions from code review

* Remove concurrency type

* Rename variable for clarity

* Add copying prerender files during export

* Add comment for clarity

* Fix exporting

* Update comment

* Add additional note

* Rename variable

* Update to not re-export SPR pages from build

* Hard navigate when fetching data fails

* Remove default extension

* Add brackets

* Add checking output files to prerender tests

* Adjust export move logic

* Clarify behavior of export aggregation

* Update variable names for clarity

* Update tests

* Add comment

* s/an oxymoron/contradictory/

* rename

* Extract error case

* Add tests for exporting SPR pages and update
/_next/data endpoint to end with .json

* Relocate variable

* Adjust route building

* Rename to unstable

* Rename unstable_getStaticParams

* Fix linting

* Only add this when a data request

* Update prerender data tests

* s/isServerless/isLikeServerless/

* Don't rely on query for `next start` in serverless mode

* Rename var

* Update renderedDuringBuild check

* Add test for dynamic param with bracket

* Fix serverless next start handling

* remove todo

* Adjust comment

* Update calculateRevalidate

* Remove cache logic from render.tsx

* Remove extra imports

* Move SPR cache logic to next-server

* Remove old isDynamic prop

* Add calling App getInitialProps for SPR pages

* Update revalidate logic

* Add isStale to SprCacheValue

* Update headers for SPR

* add awaiting pendingRevalidation

* Dont return null for revalidation render

* Adjust logic

* Be sure to remove coalesced render

* Fix data for serverless

* Create a method coalescing utility

* Remove TODO

* Extract send payload helper

* Wrap in-line

* Move around some code

* Add tests for de-duping and revalidating

* Update prerender manifest test

* Global CSS Support

* Fix webpack configuration

* oneOf rule isn't necessary yet

* Adjust CSS chunk naming

* Begin testing CSS behavior

* Add another test TODO

* Replace null-loader with ignore-loader

* Turn on chunks for new CSS feature

* Fix multi test suite

* Test CSS import order

* Test style HMR

* Test CSS compilation

* Test compilation and prefixing together

* Verify CSS styling works for Development and Production

* Add missing TODO

* Remove unnecessary test

* Adjust TODO message

* Hide page until React hydrates

* Revert "Hide page until React hydrates"

This reverts commit 898d4e0ee547b003d5790e2b11476740d645b907.

* Hide FOUC during development

* Test CSS imports

* Update tests TODO

* Add fixture for url() test

* Test `file-loader` support in CSS files

* Use a simple variant of cssnano

* Self-import

* Undo bundling

* Implement suggestion

* Add link to docs for prerender indicator and allow disabling

* Fix lint error from example

* Disable by default when electron is detected

* Add button to dismiss indicator for session

* Update disabling indicator in electron

* Add autoExport to __NEXT_DATA__

* Update render variable

* Initial move

* Make emitting work

* Update paths

* Remove leftover files

* Add correct externals configuration

* Import correct path

* Update path to work with ts-server test

* Update lib directory

* Compile next-server/lib