Extract UI elements from storybook into new ui crate (#3008)

This PR extracts the various UI elements from the `storybook` crate into
a new `ui` library crate.

Release Notes:

- N/A

Cargo.lock

@@ -7397,6 +7397,7 @@ dependencies = [
  "settings",
  "simplelog",
  "theme",
+ "ui",
  "util",
 ]
 
@@ -8599,6 +8600,17 @@ version = "0.1.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ed646292ffc8188ef8ea4d1e0e0150fb15a5c2e12ad9b8fc191ae7a8a7f3c4b9"
 
+[[package]]
+name = "ui"
+version = "0.1.0"
+dependencies = [
+ "anyhow",
+ "gpui2",
+ "serde",
+ "settings",
+ "theme",
+]
+
 [[package]]
 name = "unicase"
 version = "2.7.0"