Blender Git Loki

Cryptomatte: Flexible Definition of CryptomatteLayers.

Cryptomatte layers in Blender are predefined. Other render engines
might have other naming schemes. This patch will allow creation of
cryptomatte layers with other names. This will be used by D3959 to
load cryptomatte openexr files from other render engines.

EEVEE and Cycles still use our fix naming scheme so no changes are
detectable by users.