Allow switching how content is dropped

[mjbvz]

Related to #156384

When multiple drop providers are registered, we should allow selecting which one is used on drop. This includes letting users fall back to dropping the item as plaintext

Main requirements:

• When dropping into an editor, if multiple drop edits are returned, apply the best automatically by default but then show some sort of UI to change how the contents are dropping
• Add a setting so that users can configure the default drop provider per language

[mjbvz]

Learnings from this also apply to copy paste providers

Will likely require some API additions to:

• Give drops a human readable name to show in the UI
• Give drops a id that we can use in the settings

[mjbvz]

This has been implemented using the editor.dropIntoEditor.preferences setting and drop into UI

Tracking finalization for the related extension API in #30066

[mjbvz]

To verify:

• In a md file, try dragging and dropping a file from the VS Code explorer into the editor. Confirm you can use the drop widget to change how it is inserted

• Now set editor.dropIntoEditor.preferences to something like [ "uri.absolute" ]. Confirm that dropping into markdown now inserts the full path by default but you can still use the widget to change drop types