Cbor follow up fixes

[TingDaoK]

Issue #, if available:

• Fixes after merge
  • typo: AWS_CBOR_TYPE_UNKOWN->AWS_CBOR_TYPE_UNKNOWN
  • aws_cbor_decoder_new takes aws_byte_cursor by value instead of pointer
  • renaming aws_cbor_decoder_release -> aws_cbor_decoder_destroy
  • Fixed a bug of aws_byte_buf_reserve_smart that forgets to check if no expansion needs or not and added test for it
• for sure, shall not make a PR that is too long and sit in review for too long.

Description of changes:

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