Align DFD type names with spec

[LPGhatguy]

Currently, some of the types related to Data Format Descriptors (DFDs) don't quite align with the KTX and KDF specifications. I propose that a couple types are renamed:

• Reader::data_format_descriptors -> Reader::data_format_descriptor_blocks OR Reader::dfd_blocks
• DataFormatDescriptor -> DataFormatDescriptorBlock OR DfdBlock
• DataFormatDescriptorHeader -> DataFormatDescriptorHeaderBlock OR DfdBlockHeader

A KTX2 two file has one data format descriptor, containing multiple data format descriptor blocks.

The full name "data format descriptor block" is very long, so it might be preferable to use DFD, an abbreviation used frequently in the spec. These types can be affixed with references to the KTX spec or the Khronos Data Format spec, which has detail that I think is very useful.

• BasicDataFormatDescriptorHeader -> BasicDataFormatDescriptorBlockHeader OR BasicDfdBlockHeader OR DfdBlockHeaderBasic

Thought process is similar here to the other types. It might be more clear to use the name DfdBlockHeaderBasic because this type is the header for some data contained within a DFD block.

Any other types that reference DFDs (plural) would be changed to reference DFD blocks.

[Ralith]

I'm on board with all of this, favoring the contraction to DFD where applicable.

It might be more clear to use the name DfdBlockHeaderBasic because this type is the header for some data contained within a DFD block.

I don't quite see how this is clearer, though the impact on sorting/autocomplete is arguably positive regardless.