Widgets: Allow filtering args in `the_widget`

[noisysocks]

Originally reported in ​https://github.com/WordPress/gutenberg/issues/36830.

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### Description

currently it's not possible to change widgets before_title from <h2> to <h4> when you use new gutenberg widgets environment and legacy widgets like nav_menu
it's calling the_widget with $arg without any apply_filter in wp-includes/blocks/legacy-widget.php

### Step-by-step reproduction instructions

1. Go to /wp-admin/widgets.php
2. add Legacy Widget - Navigation Menu
3. Enter some title
4. On frontend it will be rendered as <h2> but there is no way how to change it to something else, like <h4> - no hook

### Screenshots, screen recording, code snippet

_No response_

### Environment info

_No response_

### Please confirm that you have searched existing issues in the repo.

Yes

### Please confirm that you have tested with all plugins deactivated except Gutenberg.

Yes

[noisysocks]

Adding a new the_widget_args filter to the_widget makes sense to me.

$args = apply_filters( 'the_widget_args', $args, $instance, $widget );

[kajalgohel]

Added the Filter for the_widget()