Issues when using a composition that varies by culture in a non variant document type

[lauraneto]

Which Umbraco version are you using?

17.0.0-rc1

Bug summary

While updating a test site from v16 to v17 I found two issues when using a composition that varies by culture in a non variant document type. I'm not sure if the main cause is the same or not, so if needed please create a separate issue.

1. When opening the document, the values of the properties of the composition do not load in the UI, even though they come through in the API

2. When using a toggle (not sure if this affects more types, but it doesn't seem to affect Textstring), the FE tries to send the value in all of the backoffice cultures, even though the document is invariant, causing an error in the API

Specifics

No response

Steps to reproduce

1. Create a project in Umbraco 17.
2. Create a new document type "Composition", with a text string property "Text" (with "Shared across cultures" is disabled) and enable "Allow vary by culture".
3. Create a new document type "Home", select the previously created composition, enable "Allow at root" and leave "Allow vary by culture" disabled.
4. Create a new document using the Home type, type in "TEXT" in the text field and publish.
5. Refresh the page and verify that the value is gone.

For reproducing issue 2, add a toggle (true/false) property to the composition.

Expected result / actual result

Actual: The values are missing and in some cases errors are thrown by the API
Expected: The saved values are displayed in the document and no errors are thrown when publishing

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This item has been added to our backlog AB#61672