Fix saved searches to remove additional invalid characters from labels:
* Remove repeated spaces or underscores.
* Remove leading and trailing spaces or underscores.
* Normalize Unicode characters to NFC form.
Also add a fix script to renormalize labels in old saved searches. A few
problems with existing searches:
* Some saved searches somehow had labels containing NULL elements.
* Some had leading or trailing underscores.
* Some had repeated underscores.
* Some had non-English characters in uppercase.
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