[PEICH] Adding check to whether perseus markdown is accessible. (#2692)

## Summary:
Updated our `isItemAccessible` function to include a check to confirm our markdown is accessible. Which ammounts to checking if markdown images include alt text. If it does not the item is considered inaccessible.

Issue: LEMS-3106

## Test plan:
Run `pnpm test` and all tests should return as passing.

Author: catandthemachines

Reviewers: catandthemachines, jeremywiebe, tatianasnook

Required Reviewers:

Approved By: jeremywiebe, tatianasnook

Checks: ✅ 8 checks were successful

Pull Request URL: #2692

Author: catandthemachines

.changeset/twelve-plants-doubt.md

@@ -0,0 +1,5 @@
+---
+"@khanacademy/perseus-core": patch
+---
+
+Adding extra check to accessible markkdown in isItemAccessible.

packages/perseus-core/.eslintrc.js

@@ -17,7 +17,6 @@ module.exports = {
             "@khanacademy/perseus-linter",
             "@khanacademy/perseus-score",
             "@khanacademy/pure-markdown",
-            "@khanacademy/simple-markdown",
         ],
     },
 };

packages/perseus-core/package.json

@@ -27,6 +27,7 @@
     "dependencies": {
         "@khanacademy/kas": "workspace:*",
         "@khanacademy/perseus-utils": "workspace:*",
+        "@khanacademy/simple-markdown": "workspace:*",
         "tiny-invariant": "catalog:prodDeps"
     },
     "devDependencies": {
@@ -39,4 +40,4 @@
         "underscore": "catalog:peerDeps"
     },
     "keywords": []
-}
+}