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)))}}
```

plugins/chat/assets/javascripts/discourse/components/chat-emoji-picker.hbs

@@ -25,7 +25,7 @@
           )
         }}
         @value={{this.chatEmojiPickerManager.picker.initialFilter}}
-        @filterAction={{action this.didInputFilter value="target.value"}}
+        @filterAction={{with-event-value this.didInputFilter}}
         @icons={{hash left="search"}}
         @containerClass="chat-emoji-picker__filter"
         autofocus={{true}}

plugins/chat/assets/javascripts/discourse/components/chat/modal/create-channel.hbs

@@ -17,7 +17,7 @@
         class="chat-modal-create-channel__input"
         @type="text"
         @value={{this.name}}
-        {{on "input" (action this.onNameChange value="target.value")}}
+        {{on "input" (with-event-value this.onNameChange)}}
       />
     </div>
 

plugins/chat/assets/javascripts/discourse/components/chat/modal/edit-channel-description.hbs

@@ -14,10 +14,7 @@
       @max={{this.descriptionMaxLength}}
     >
       <textarea
-        {{on
-          "input"
-          (action this.onChangeChatChannelDescription value="target.value")
-        }}
+        {{on "input" (with-event-value this.onChangeChatChannelDescription)}}
         class="chat-modal-edit-channel-description__description-input"
         placeholder={{i18n
           "chat.channel_edit_description_modal.input_placeholder"

plugins/styleguide/assets/javascripts/discourse/components/sections/molecules/char-counter.hbs

@@ -1,10 +1,7 @@
 <StyleguideExample @title="<CharCounter>">
   <CharCounter @max="50" @value={{@dummy.charCounterContent}}>
     <textarea
-      {{on
-        "input"
-        (action (mut @dummy.charCounterContent) value="target.value")
-      }}
+      {{on "input" (with-event-value (fn (mut @dummy.charCounterContent)))}}
       class="styleguide--char-counter"
     ></textarea>
   </CharCounter>