feat(function): add allowedInArgument instead of greediness property (#2134)

* Remove `greediness` property

Use boolean `grouped` property instead, which is more consistent with 
LaTeX.

BREAKING CHANGE: \cfrac, \color, \textcolor, \colorbox, \fcolorbox are 
no longer grouped.

* Rename grouped to allowedInArgument

* Reenable tests

* Update documentation

* Fix typo

Co-authored-by: Kevin Barabash <kevinb@khanacademy.org>

src/defineEnvironment.js

@@ -52,7 +52,6 @@ export type EnvSpec<NODETYPE: NodeType> = {|
     type: NODETYPE, // Need to use the type to avoid error. See NOTES below.
     numArgs: number,
     argTypes?: ArgType[],
-    greediness: number,
     allowedInText: boolean,
     numOptionalArgs: number,
     handler: EnvHandler,
@@ -99,7 +98,6 @@ export default function defineEnvironment<NODETYPE: NodeType>({
     const data = {
         type,
         numArgs: props.numArgs || 0,
-        greediness: 1,
         allowedInText: false,
         numOptionalArgs: 0,
         handler,