feat: Support \phase (#2406)

* Support \phase

* Update screenshots

* Update documentation

* Add a11y test

* Edit MathML notation to phasorangle

* Move code to enclose.js

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

docs/support_table.md

@@ -816,7 +816,7 @@ use `\ce` instead|
 |\partial|$\partial$||
 |\perp|$\perp$||
 |\phantom|$\Gamma^{\phantom{i}j}_{i\phantom{j}k}$|`\Gamma^{\phantom{i}j}_{i\phantom{j}k}`|
-|\phase|<span style="color:firebrick;">Not supported</span>||
+|\phase|$\phase{-78^\circ}$|`\phase{-78^\circ}`|
 |\Phi|$\Phi$||
 |\phi|$\phi$||
 |\Pi|$\Pi$||

docs/supported.md

@@ -212,6 +212,7 @@ For Persian composite characters, a user-supplied [plug-in](https://github.com/
 |$\xcancel{ABC}$ `\xcancel{ABC}`|$\not =$ `\not =`
 |$\sout{abc}$ `\sout{abc}`|$\boxed{\pi=\frac c d}$ `\boxed{\pi=\frac c d}`
 |$a_{\angl n}$ `$a_{\angl n}`|$a_\angln$ `a_\angln`
+|$\phase{-78^\circ}$`\phase{-78^\circ}` |
 
 `\tag{hi} x+y^{2x}`
 $$\tag{hi} x+y^{2x}$$