priceFloors & PBS adapter: support mediaType and size specific floors

[dgirardi]

Type of change

• Feature

Description of change

• Updated priceFloors to pass a 3rd argument {size, mediaType} to inverseCpmAdjustment
• Updated ORTB converter to ask for specific floors for each mediatype and banner size. If these are different from imp.bidfloor, they're set to ext.bidfloor & ext.bidfloorcur under native/video/banner and each format in banner.format.
• Updated the PBS adapter to aggregate granular floors in a similar way to imp.bidfloor (in case floors are different across bidders).

Other information

Closes #12308