Corrects styling on Buttons that only have a count and icon (#5448)

* adds 'count' prop to IconButton

* adds VRT for IconButton with trailing counter

* updates IconButton component API docs

* adds changeset

* test(vrt): update snapshots

* adds 'count' to IconButton Playground story

* addresses feedback to modify component API

* modifies changeset

* reverts new IconButton VRT

* reverts new IconButton stories

* test(vrt): update snapshots

* appeases the linter

* add vrt

* test(vrt): update snapshots

---------

Co-authored-by: mperrotti <mperrotti@users.noreply.github.com>
Co-authored-by: Katie Langerman <18661030+langermank@users.noreply.github.com>
Co-authored-by: langermank <langermank@users.noreply.github.com>

Author: mperrotti

.changeset/brave-penguins-clap.md

@@ -0,0 +1,5 @@
+---
+"@primer/react": minor
+---
+
+Corrects horizontal padding of `<Button>` when the button only contains an icon and a counter label (no button text label).