Bugfix/inline editing provisional drafts

[i-just]

Description

Replication steps:

• create a section with an entry type that has a required plain text field
• add an entry to it, fill out the plain text field and save
• now edit that entry again, change the title, let it auto-save and leave it in a provisional draft state
• go to the index page for the section (in a table view) and click “Edit” to activate inline editing
• remove the copy from the plain text field and try to save
• a generic “Server error occurred” is displayed

Solution:
When getting the edited entries by their IDs, get the provisional drafts, too. When composing an array of errors to be passed back to JS, index the errors by canonical ID (as that’s what’s used in the data-id attribute for element rows).

Note: when inline editing a provisional draft, the changes will be applied to the provisional draft, not the canonical element.

Related issues

n/a (found by Luke)