feat: Add margin around zoomToFit (google#6042)

* Add margin around zoomToFit

* Change configurable property to fixed constant.

* VS Code keeps indenting stuff for no reason.

core/workspace_svg.js

@@ -116,6 +116,12 @@ goog.require('Blockly.MetricsManager');
 goog.require('Blockly.Msg');
 
 
+/**
+ * Margin around the top/bottom/left/right after a zoomToFit call.
+ * @const
+ */
+const ZOOM_TO_FIT_MARGIN = 20;
+
 /**
  * Class for a workspace.  This is an onscreen area with optional trashcan,
  * scrollbars, bubbles, and dragging.
@@ -2168,8 +2174,9 @@ class WorkspaceSvg extends Workspace {
     let workspaceWidth = metrics.viewWidth;
     let workspaceHeight = metrics.viewHeight;
     const blocksBox = this.getBlocksBoundingBox();
-    let blocksWidth = blocksBox.right - blocksBox.left;
-    let blocksHeight = blocksBox.bottom - blocksBox.top;
+    const doubleMargin = ZOOM_TO_FIT_MARGIN * 2;
+    let blocksWidth = blocksBox.right - blocksBox.left + doubleMargin;
+    let blocksHeight = blocksBox.bottom - blocksBox.top + doubleMargin;
     if (!blocksWidth) {
       return;  // Prevents zooming to infinity.
     }