DEV: Introduce a helper for handling events (#25433)

Instead of

```hbs
{{on "input" (action this.foo value="target.value")}}
{{on "input" (action (mut this.bar) value="target.value")}}
```

you can use:

```hbs
{{on "input" (with-event-value this.foo)}}
{{on "input" (with-event-value (fn (mut this.bar)))}}
```

or in gjs:

```gjs
import { fn } from "@ember/helper";
import { on } from "@ember/modifier";
import withEventValue from "discourse/helpers/with-event-value";
…
{{on "input" (withEventValue (fn (mut this.bar)))}}
```

app/assets/javascripts/admin/addon/templates/dashboard_reports.hbs

@@ -6,7 +6,7 @@
         class="filter-reports-input"
         placeholder={{i18n "admin.dashboard.filter_reports"}}
         autofocus={{true}}
-        {{on "input" (action "filterReports" value="target.value")}}
+        {{on "input" (with-event-value this.filterReports)}}
       />
     </div>