Proposal: norm16-{filterable,resolve} extensions

[teoxoy]

Proposal to add 2 extensions that enable filtering and resolve respectively for the following formats:

• r16unorm
• r16snorm
• rg16unorm
• rg16snorm
• rgba16unorm
• rgba16snorm

Note that both extensions depend on formats-tier-1.

Extensions:

• norm16-filterable

  Metal: Available
  D3D FL11: Available
  Vulkan: Needs SAMPLED_IMAGE_FILTER_LINEAR (loses Samsung Xclipse 920 and a lot of Mali devices + all Adreno 5XX devices due to formats-tier-1)

• norm16-resolve

  Metal: Available only on Mac2
  D3D FL11: Available
  Vulkan: Available

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We don't seem to have precedent for dependant extensions. We can either require that usage of these extensions also requires the user to enable formats-tier-1 or enable formats-tier-1 automatically.

[kainino0x]

Note: this new feature would be dependent on another new feature from #3001 or #3837.