rustdoc: when opening the settings popover, reload it

This way, if something else (or another page) changes the setting,
it's reflected in the popover.

Author: notriddle

tests/rustdoc-gui/sidebar-resize-setting.goml

@@ -0,0 +1,24 @@
+// Checks sidebar resizing stays synced with the setting
+go-to: "file://" + |DOC_PATH| + "/test_docs/index.html"
+assert-property: (".sidebar", {"clientWidth": "200"})
+show-text: true
+
+// Verify that the "hide" option is unchecked
+click: "#settings-menu"
+wait-for: "#settings"
+assert-css: ("#settings", {"display": "block"})
+assert-property: ("#hide-sidebar", {"checked": "false"})
+press-key: "Escape"
+wait-for-css: ("#settings", {"display": "none"})
+
+drag-and-drop: ((205, 100), (5, 100))
+assert-css: (".sidebar", {"display": "none"})
+
+// Verify that the "hide" option is checked
+focus: "#settings-menu a"
+press-key: "Enter"
+wait-for-css: ("#settings", {"display": "block"})
+assert-property: ("#hide-sidebar", {"checked": "true"})
+click: "#hide-sidebar"
+assert-property: ("#hide-sidebar", {"checked": "false"})
+assert-css: (".sidebar", {"display": "block"})