Revise metadata semantics yang module for INT v2

[mickeyspiegel]

• Rename p4-dtel-metadata-semantics.yang to p4-int-metadata-semantics.yang
  • Align with strategy to call all aspects and variants part of INT
• Replace per metadata field groupings with generic grouping that
  can be used for metadata semantics details of all fields
  • Add identity statements for each baseline metadata field
  • Add identity statements for three common domain specific fields
    • flow_id
    • sequence_number
    • mac_address
  • Move leafs that apply to specific metadata fields to the generic
    grouping, conditioning the leafs using "when" statements
  • Move node-id to generic grouping, conditioning this leaf
    when the metadata field is node_id
  • Remove grouping for identifiers since this is moved to generic per
    metadata field groupings
  • Add grouping for domain specific metadata details including
    • size in 4-byte words
    • INT-MX properties as defined in INT 2.1
• Add nested groupings for domain specific ids, along with bit
  position and identity reference for each domain specific metadata
  field associated with each domain

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