fix: fix positioning of block comments in RTL mode (#249)

* fix: fix positioning of block comments in RTL mode

* chore: factor out shared constant

Author: gonfunko

src/scratch_comment_bubble.ts

@@ -129,15 +129,19 @@ export class ScratchCommentBubble
   }
 
   dropAnchor() {
-    this.moveTo(this.anchor.x + 40, this.anchor.y - 16);
+    const verticalOffset = 16;
+    this.moveTo(
+      this.anchor.x + 40 * (this.workspace.RTL ? -1 : 1),
+      this.anchor.y - verticalOffset
+    );
     const location = this.getRelativeToSurfaceXY();
     this.anchorChain = Blockly.utils.dom.createSvgElement(
       Blockly.utils.Svg.LINE,
       {
         x1: this.anchor.x - location.x,
         y1: this.anchor.y - location.y,
-        x2: this.getSize().width / 2,
-        y2: 16,
+        x2: (this.getSize().width / 2) * (this.workspace.RTL ? -1 : 1),
+        y2: verticalOffset,
         style: `stroke: ${this.sourceBlock.getColourTertiary()}; stroke-width: 1`,
       },
       this.getSvgRoot()