Shared webforms return HTTP 403 when there is no dedicated URL

Problem/Motivation

Using webform_share to embed a form via the /webform/{webform}/share.js route, a '403 Forbidden' response is returned when the form page setting (e.g. Allow users to post submissions from a dedicated URL) is disabled.

Steps to reproduce

• Check 'Form sharing enabled' (from the webform_share submodule)
• Uncheck 'Allow users to post submissions from a dedicated URL'
• Embed the webform on a host page using the JavaScript option (e.g. <script src="//d9.test/webform/share_test/share.js"></script>)
• The webform will not be embedded on the host page, and developer tools will show a 403 response for the /webform/share_test/share.js URL.

Proposed resolution

Change the _entity_access route requirement from webform.submission_page to webform.submission_create for the entity.webform.share_script route.

This seems OK because the entity.webform.share_page.javascript route, which the share script itself embeds for the iframe src, uses webform.submission_create.