fix: measure/drawing tooltip was misplaced (#2541)

Broken since 70f87d8636

fix #2539

Before:


![image](https://github.com/user-attachments/assets/5e68628c-a9f7-422a-b4b9-dd5daf0d77cd)


After:


![image](https://github.com/user-attachments/assets/c1857ab2-a8d1-43eb-a3d0-11bb24286bd6)

umap/static/umap/js/modules/ui/base.js

@@ -4,6 +4,8 @@ export class Positioned {
       this.anchorTop(anchor)
     } else if (anchor && position === 'bottom') {
       this.anchorBottom(anchor)
+    } else {
+      this.anchorAbsolute()
     }
   }
 
@@ -31,6 +33,15 @@ export class Positioned {
     })
   }
 
+  anchorAbsolute() {
+    const left =
+      this.parent.offsetLeft +
+      this.parent.clientWidth / 2 -
+      this.container.clientWidth / 2
+    const top = this.parent.offsetTop + 75
+    this.setPosition({ top: top, left: left })
+  }
+
   getPosition(el) {
     return el.getBoundingClientRect()
   }