Problem/Motivation
The feature to configure placeholder texts in the Views UI was added in [2917594]. However, these placeholders are not translatable because the config schema was set to "string" (not translatable) instead of "label" (translatable).
Proposed resolution
Fix the config schema to make placeholders translatable.
Remaining tasks
Review, possibly test.
Do we need to add an update hook that transfers the default language placeholders into any existing views translations?
> No we don't