file_icons: Add separate icon key for Bicep files (#24757)

This PR adds support for bicep file icon:

Release Notes:

- Icon themes: Added the ability to change the file icon for Bicep
(`.bicep`) files.

assets/icons/file_icons/file_types.json

@@ -18,6 +18,7 @@
     "bash_logout": "terminal",
     "bash_profile": "terminal",
     "bashrc": "terminal",
+    "bicep": "bicep",
     "bmp": "image",
     "c": "c",
     "c++": "cpp",