Apply cursor styles during paint

This makes the editor's cursor an IBeam and properly deals with nested cursor styles.

Co-Authored-By: Antonio Scandurra <me@as-cii.com>

assets/themes/dark.json

@@ -89,10 +89,6 @@
         "top": 7
       }
     },
-    "margin": {
-      "bottom": 52,
-      "top": 52
-    },
     "shadow": {
       "blur": 16,
       "color": "#00000052",
@@ -158,6 +154,13 @@
         "right": 8
       }
     },
+    "modal": {
+      "margin": {
+        "bottom": 52,
+        "top": 52
+      },
+      "cursor": "Arrow"
+    },
     "left_sidebar": {
       "width": 30,
       "background": "#1c1c1c",

assets/themes/light.json

@@ -89,10 +89,6 @@
         "top": 7
       }
     },
-    "margin": {
-      "bottom": 52,
-      "top": 52
-    },
     "shadow": {
       "blur": 16,
       "color": "#0000001f",
@@ -158,6 +154,13 @@
         "right": 8
       }
     },
+    "modal": {
+      "margin": {
+        "bottom": 52,
+        "top": 52
+      },
+      "cursor": "Arrow"
+    },
     "left_sidebar": {
       "width": 30,
       "background": "#f8f8f8",