Add bash completion support for "brew switch"
Add bash completion support for "brew switch"

First autocompletes on the names of installed packages and then
autocompletes on available versions for that specific package

Closes Homebrew/homebrew#25051.

Signed-off-by: Jack Nagel <43386ce32af96f5c56f2a88e458cb94cebee3751@gmail.com>

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