UI: fix the maximum search length of Hotkeys Filter

The "fullName" property was filled only in case of exceeding
TRUNCATE_TEXT_LENGTH. Also search function had worked only with
item->text() what was the reason of maximum search length in
Hotkeys Filter(Setting->Hotkeys).

The following changes allow to search in filter without
the length limit of string along with the current functionality.
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Gitea Version: 1.28.0+dev-477-g8b6ad49a5f