feat: Case-insensitive search for non-ASCII chat and contact names (#7477)

This makes `Contact::get_all()` and `Chatlist::try_load()` case-insensitive for non-ASCII chat and
contact names as well. The same approach as in f6f4ccc6ea "feat:
Case-insensitive search for non-ASCII messages (#5052)" is used: `chats.name_normalized` and
`contacts.name_normalized` colums are added which store lowercased/normalized names (for a contact,
if the name is unset, it's a normalized authname). If a normalized name is the same as the
chat/contact name, it's not stored to reduce the db size. A db migration is added for 10000 random
chats and the same number of the most recently seen contacts, for users it will probably migrate all
chats/contacts and for bots which may have more data it's not important.

src/tools.rs

@@ -779,6 +779,15 @@ pub(crate) fn to_lowercase(s: &str) -> Cow<'_, str> {
     }
 }
 
+/// Returns text for storing in special db columns to make case-insensitive search possible for
+/// non-ASCII messages, chat and contact names.
+pub(crate) fn normalize_text(text: &str) -> Option<String> {
+    if text.is_ascii() {
+        return None;
+    };
+    Some(text.to_lowercase()).filter(|t| t != text)
+}
+
 /// Increments `*t` and checks that it equals to `expected` after that.
 pub(crate) fn inc_and_check<T: PrimInt + AddAssign + std::fmt::Debug>(
     t: &mut T,