This PR was squashed before being merged into the 3.4 branch (closes#10322).Discussion----------[WCM] Encore updates for Webpack 4Phew! The next (unreleased) version of Webpack Encore (will be 0.21.0) that supports Webpack 4 will contain a few minor changes, that have major implications on the documentation. Ultimately, I think the experience will be easier for users :). The 3 big changes are:1) In all cases, people should use the new WebpackEncoreBundle and its 2 new Twig functions - `encore_entry_script_tags()` and `encore_entry_link_tags()` to render their `script` and `link` tags.2) In earlier versions, an extra `manifest.js` file was output when using `createdSharedEntry()`. But now, a new `runtime.js` file is *always* output. But, because of the `encore_entry_script_tags()` shortcut... that's just rendered for you automatically.3) `createSharedEntry()` is no longer hipster ;). This is from changes in Webpack. A newer, and better "split chunks" feature replaces it... which (other than changing how existing users think), is much simpler. Basically, the user does nothing... except call `encore_entry_script_tags()`. But, when this feature is enabled, the final `.js` and `.css` files may be split into multiple files. And so, the `encore_entry_script_tags()` (and also the link version) may render *multiple* script tags. This all happens automatically.TODO: Wait for the bundle to be tagged, then test the new recipe (symfony/recipes#458) and code through some of the docs to catch any mistakes (due to so many changes).**Merging into 4.1 TODOS*** update `web/` to `public/`Cheers!Commits-------12ca7d9 adding a small entry about ajax code splitting165432f fixing build errorsbf649ab Documenting copyFiles() and a few small things6833bb6 finishing read-throughc2b36a2 more work on encore53f9ffe Adding docs for runtime.js and fixed a few other things62f322e documenting the new split chunks and Twig helper functions for Encore