cmd/search: notification on attempted regex searches
cmd/search: notification on attempted regex searches

Closes Homebrew/homebrew#38760.

Signed-off-by: Mike McQuaid <a17fed27eaa842282862ff7c1b9c8395a26ac320@mikemcquaid.com>

Linuxbrew/brew,maxim-belkin/brew,mahori/brew,AnastasiaSulyagina/brew,reitermarkus/brew,tonyg/homebrew,muellermartin/dist,mistydemeo/homebrew,konqui/brew,rwhogg/brew,claui/brew,mgrimes/brew,maxim-belkin/brew,konqui/brew,JCount/brew,konqui/brew,aw1621107/brew,vitorgalvao/brew,nandub/brew,rwhogg/brew,amar-laksh/brew_sudo,AnastasiaSulyagina/brew,DomT4/brew,maxim-belkin/brew,DomT4/brew,JCount/brew,nandub/brew,bfontaine/brew,reitermarkus/brew,nandub/brew,mgrimes/brew,amar-laksh/brew_sudo,reitermarkus/brew,ilovezfs/brew,Linuxbrew/brew,palxex/brew,claui/brew,jmsundar/brew,gregory-nisbet/brew,reelsense/brew,aw1621107/brew,toonetown/homebrew,Homebrew/brew,zmwangx/brew,sjackman/homebrew,EricFromCanada/brew,zmwangx/brew,tonyg/homebrew,mahori/brew,gregory-nisbet/brew,konqui/brew,claui/brew,reitermarkus/brew,alyssais/brew,gordonmcshane/homebrew,mistydemeo/homebrew,toonetown/homebrew,Homebrew/brew,toonetown/homebrew,palxex/brew,zmwangx/brew,reelsense/brew,Linuxbrew/brew,JCount/brew,ilovezfs/brew,alyssais/brew,gregory-nisbet/brew,pseudocody/brew,jmsundar/brew,hanxue/linuxbrew,bfontaine/brew,JCount/brew,vitorgalvao/brew,Homebrew/brew,Linuxbrew/brew,reelsense/brew,DomT4/brew,EricFromCanada/brew,MikeMcQuaid/brew,vitorgalvao/brew,aw1621107/brew,rwhogg/brew,sjackman/homebrew,mahori/brew,staticfloat/brew,staticfloat/brew,MikeMcQuaid/brew,sjackman/homebrew,mgrimes/brew,MikeMcQuaid/brew,alyssais/brew,mistydemeo/homebrew,hanxue/linuxbrew,DomT4/brew,pseudocody/brew,EricFromCanada/brew,amar-laksh/brew_sudo,muellermartin/dist,vitorgalvao/brew,nandub/brew,bfontaine/brew,pseudocody/brew,sjackman/homebrew,hanxue/linuxbrew,tonyg/homebrew,Homebrew/brew,gordonmcshane/homebrew,mahori/brew,MikeMcQuaid/brew,jmsundar/brew,gordonmcshane/homebrew,AnastasiaSulyagina/brew,EricFromCanada/brew,staticfloat/brew,claui/brew,muellermartin/dist,palxex/brew,ilovezfs/brew