feat(icons): add square-dimensions (#4547)

* feat(icons): add aspect-ratio

Adds an aspect-ratio icon: a frame with two opposing corner brackets,
depicting the proportions of a frame rather than the frame itself.

Distinct from ratio, which is two overlapping rects showing portrait and
landscape orientation, and from the scan / minimize / maximize family,
which use four corner brackets rather than two.

* feat(icons): rename aspect-ratio to square-dimensions

Per review on #4547 (@karsa-mistmere, @ericfennis): the primary shape is
a square, so it takes the square-<x> name, and square-dimensions reads
more naturally for setting width/height than the ratio-specific
aspect-ratio. Retunes tags and use-cases toward size/dimensions.

* Update icons/square-dimensions.json

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

* Update icons/square-dimensions.json

---------

Co-authored-by: Eric Fennis <eric.fennis@gmail.com>
Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Karsa <contact@karsa.org>

icons/square-dimensions.json

@@ -0,0 +1,31 @@
+{
+  "$schema": "../icon.schema.json",
+  "contributors": [
+    "samuelalake"
+  ],
+  "use-cases": [
+    "setting or displaying the width and height of a frame or object",
+    "a size or dimensions control in a design or layout editor",
+    "indicating fixed-size mode for an element",
+    "representing artboard or canvas size settings",
+    "labeling size presets or templates in a design system"
+  ],
+  "tags": [
+    "ratio",
+    "size",
+    "width",
+    "height",
+    "resize",
+    "scale",
+    "frame",
+    "proportions",
+    "aspect",
+    "bounds",
+    "measurements",
+    "canvas"
+  ],
+  "categories": [
+    "design",
+    "layout"
+  ]
+}

icons/square-dimensions.svg

@@ -0,0 +1,15 @@
+<svg
+  xmlns="http://www.w3.org/2000/svg"
+  width="24"
+  height="24"
+  viewBox="0 0 24 24"
+  fill="none"
+  stroke="currentColor"
+  stroke-width="2"
+  stroke-linecap="round"
+  stroke-linejoin="round"
+>
+  <rect width="18" height="18" x="3" y="3" rx="2" />
+  <path d="M12 7H7v5" />
+  <path d="M12 17h5v-5" />
+</svg>