Add explicit dependency on tabbable. (#691)

* Add explicit dependency on tabbable.

This project directly imports tabbable, but relies on it being available
transitively through its dependency on focus-trap. This makes this
package incompatible with yarn v2/v3, which requires that packages
explicitly state all dependencies.

It's also, more generally, best practice to explicitly declare all
dependencies. This helps ensure that package managers provide the
appropriate versions of dependencies to their requesting packages.

* Clarify why the added dependency

Co-authored-by: Stefan Cameron <stefan@stefcameron.com>

.changeset/strange-mirrors-serve.md

@@ -0,0 +1,5 @@
+---
+'focus-trap-react': patch
+---
+
+Add explicit dependency on tabbable since the source directly requires it.

package.json

@@ -95,7 +95,8 @@
     "typescript": "^4.7.3"
   },
   "dependencies": {
-    "focus-trap": "^6.9.4"
+    "focus-trap": "^6.9.4",
+    "tabbable": "^5.3.3"
   },
   "peerDependencies": {
     "prop-types": "^15.8.1",