Are extracts considered alchemical items for the purposes of swift alchemy?
And what about mutagens and bombs?
Do this items benefit from the halved creation time?
No. Alchemical Items are a specifically defined class of items that require a Craft (Alchemy) check to create. Examples include Alchemist's Fire, Acid, Poisons, Smelling Salts, Smokesticks, etc. Further examples can be found here, here, and here
Potions are considered Magic Items, and Extracts, Bombs, and Mutagens are all class features that don't require a skill check. Thus, Swift Alchemy doesn't apply to any of them.