Update Features docs

[teoxoy]

• Remove PIPELINE_STATISTICS_QUERY from WebGPU features section and update its doc comment to reflect that.
  It was removed in: Delete pipeline statistics queries gpuweb/gpuweb#2296 (got moved to the proposals folder).
• Remove ADDRESS_MODE_CLAMP_TO_BORDER from WebGPU features section and update its doc comment to reflect that.
  It was removed in: Remove clamp-to-border-color option from GPUSampler gpuweb/gpuweb#235.
• Rename WRITE_TIMESTAMP_INSIDE_PASSES to TIMESTAMP_QUERY_INSIDE_PASSES to better align it with TIMESTAMP_QUERY.
  Also add "This is a native only feature." to its doc comment.
  This feature also has its own proposal over in the gpuweb repo (with the same name).