Highlight all the message search matches

[abdullahemad12]

It is expected that when a user search for a message, that all the matches within the same messages are highlighted (if there are more than one match) not just the first match. This is also consistent with how the search in the desktop app is implemented

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Description

This commit changes the highlight strategy for message search from STRICT to MATCH_ALL. As a user, it is expected that if a message contains more than one occurrence of the key I am searching for, that all the found keys be highlighted not only the first one (which is indeed the behavior of the signal desktop app)