[FIX] full_screen_chart: prevent fullscreen chart from closing on drag-out

Steps to reproduce:

1. Open a dashboard and put a chart in fullscreen.
2. mousedown inside the chart.
3. Drag the pointer outside the chart window.
4. Release (mouseup).

Before this commit:
The fullscreen closes unexpectedly. Because mousedown and mouseup
occur on different elements, the browser dispatches the click on their
nearest common ancestor (the overlay), which had the close handler.

After this commit:

- Introduce a dedicated `.o-fullscreen-chart-backdrop` sibling and move
  the close handler there.
- Result: drag-out (down in chart, up outside) no longer closes; outside
  click (down+up on backdrop), Exit button, and `Esc` still close as expected.

closes #6991

Task: 5005933
Signed-off-by: Rémi Rahir (rar) <rar@odoo.com>

Author: dhrp-odoo

src/components/full_screen_chart/full_screen_chart.xml

@@ -1,9 +1,11 @@
 <templates>
   <t t-name="o-spreadsheet-FullScreenChart">
-    <div
-      class="position-absolute o-fullscreen-chart-overlay w-100 h-100 d-flex"
-      t-if="figureUI"
-      t-on-click="exitFullScreen">
+    <div class="position-absolute o-fullscreen-chart-overlay w-100 h-100 d-flex" t-if="figureUI">
+      <div
+        class="position-absolute top-0 start-0 end-0 bottom-0"
+        t-on-click="exitFullScreen"
+        aria-hidden="true"
+      />
       <button
         class="o-exit top-0 end-0 position-absolute o-button primary m-1"
         t-on-click="exitFullScreen">

tests/figures/chart/chart_full_screen.test.ts

@@ -1,6 +1,12 @@
 import { Model } from "../../../src";
 import { createScorecardChart, createWaterfallChart } from "../../test_helpers/commands_helpers";
-import { click, keyDown } from "../../test_helpers/dom_helper";
+import {
+  click,
+  keyDown,
+  pointerDown,
+  pointerUp,
+  triggerMouseEvent,
+} from "../../test_helpers/dom_helper";
 import { mockChart, mountSpreadsheet, nextTick } from "../../test_helpers/helpers";
 
 mockChart();
@@ -47,7 +53,7 @@ describe("chart menu for dashboard", () => {
     // Click outside of the chart in the full screen overlay
     await click(fixture, ".o-figure [data-id='fullScreenChart']");
     expect(".o-fullscreen-chart").toHaveCount(1);
-    await click(fixture, ".o-fullscreen-chart-overlay");
+    await click(fixture, ".o-fullscreen-chart-overlay > div:first-child");
     expect(".o-fullscreen-chart").toHaveCount(0);
 
     // Click the exit button in the full screen overlay
@@ -62,4 +68,26 @@ describe("chart menu for dashboard", () => {
     await keyDown({ key: "Escape" });
     expect(".o-fullscreen-chart").toHaveCount(0);
   });
+
+  test("Keeps fullscreen open when pointerdown is inside and pointerup is outside", async () => {
+    createWaterfallChart(model);
+    model.updateMode("dashboard");
+    await nextTick();
+
+    await click(fixture, ".o-figure [data-id='fullScreenChart']");
+    expect(".o-fullscreen-chart").toHaveCount(1);
+
+    const chart = fixture.querySelector(".o-fullscreen-chart")!;
+    const overlay = fixture.querySelector(".o-fullscreen-chart-overlay")!;
+    expect(chart).not.toBeNull();
+    expect(overlay).not.toBeNull();
+
+    await pointerDown(chart);
+    await pointerUp(overlay);
+
+    triggerMouseEvent(overlay, "click");
+    await nextTick();
+
+    expect(".o-fullscreen-chart").toHaveCount(1);
+  });
 });

tests/test_helpers/dom_helper.ts

@@ -121,6 +121,11 @@ export async function pointerDown(target: DOMTarget) {
   await nextTick();
 }
 
+export async function pointerUp(target: DOMTarget) {
+  triggerMouseEvent(target, "pointerup");
+  await nextTick();
+}
+
 /**
  * Simulate hovering a cell for a given amount of time.
  * Don't forget to use `jest.useFakeTimers();` when using