Allow [Search Open Tabs] to be a default search engine option

[SPFish144]

Firefox had the feature to explicitly search for tabs using a prepending `%　` in the search/address bar for a while. Additionally, when typing into the search/address bar, open tabs are indexed and presented as search entries. 

However, there is no functionality like using ctrl/cmd+shift+A in Chrome/Edge where the user may initiate an explicit tab search with one input event. It would currently take at least three inputs ([Ctrl+L], [%],[space]) to start an explicit tab search on keyboard, or two ([List all tabs] icon → [Search tabs]) on mouse.

If someone uses tab search a lot, it makes sense to be able to replace the default web search engine with local tab search so an explicit tab search only takes [Ctrl+L] just like someone else may prefer to use that shortcut to do web search.

[Jon]

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