feat: bring embed builder field manipulation in line with underlying array functionality (#3761)

* feat: splice multiple fields

* remove MessageEmbed#spliceField
* add MessageEmbed#spliceFields
* to behave more like Array#splice
* and allow multiple fields to be replaced/inserted
* update typings accordingly

* refactor: rename check to normalize

* check suggests boolean return type

* feat: allow spread args or array as field input

* rewrite: replace addField in favor of addFields

* typings: account for changes

* chore: bump min node to 11.0.0

* for Array#flat

* fix: bump min-node in package engines field

* remove addBlankField

docs/general/faq.md

@@ -3,7 +3,7 @@ These questions are some of the most frequently asked.
 
 
 ## No matter what, I get `SyntaxError: Block-scoped declarations (let, const, function, class) not yet supported outside strict mode`‽
-Update to Node.js 10.0.0 or newer.
+Update to Node.js 11.0.0 or newer.
 
 ## How do I get voice working?
 - Install FFMPEG.

docs/general/welcome.md

@@ -33,7 +33,7 @@ discord.js is a powerful [Node.js](https://nodejs.org) module that allows you to
 - 100% coverage of the Discord API
 
 ## Installation
-**Node.js 10.0.0 or newer is required.**  
+**Node.js 11.0.0 or newer is required.**  
 Ignore any warnings about unmet peer dependencies, as they're all optional.
 
 Without voice support: `npm install discordjs/discord.js`