* Move send-html function and rewrite in typescript
* Move getPageFiles and convert to ts
* Move getPageFiles and convert to ts (#5841)
* Move getPageFiles and convert to ts
# Conflicts:
# packages/next-server/server/render.js
* Fix unit tests
We don't have to check if the file already exists here, since it's always in production mode (dev overrides the readBuildId method to always be `development`) If the file is not found (error is thrown) we check if the file exists. If not we throw a helpful error. In other cases we throw the original error.
Fixes#3705Fixes#4656
- No longer automatically dedupe certain tags. Only the ones we know are *never* going to be duplicate like charSet, title etc.
- Fix `key=""` behavior, making sure that if a unique key is provided tags are deduped based on that.
For example:
```jsx
<meta property='fb:pages' content='one'>
<meta property='fb:pages' content='two'>
```
Would currently cause
```jsx
<meta property='fb:pages' content='two'>
```
### After this change:
```jsx
<meta property='fb:pages' content='one'>
<meta property='fb:pages' content='two'>
```
Then if you use next/head multiple times / want to be able to override:
```jsx
<meta property='fb:pages' content='one' key="not-unique-key">
<meta property='fb:pages' content='two' key="not-unique-key">
```
Would cause:
```jsx
<meta property='fb:pages' content='two'>
```
As `key` gets deduped correctly after this PR, similar to how React itself works.
- Replaces taskr-babel with taskr-typescript for the `next` package
- Makes sure Node 8+ is used, no unneeded transpilation
- Compile Next.js client side files through babel the same way pages are
- Compile Next.js client side files to esmodules, not commonjs, so that tree shaking works.
- Move error-debug.js out of next-server as it's only used/require in development
- Drop ansi-html as dependency from next-server
- Make next/link esmodule (for tree-shaking)
- Make next/router esmodule (for tree-shaking)
- add typescript compilation to next-server
- Remove last remains of Flow
- Move hoist-non-react-statics to next, out of next-server
- Move htmlescape to next, out of next-server
- Remove runtime-corejs2 from next-server
