bug: did.Parse() should url-decode the DID's components

[llorllale]

(followup from PR #2288 )

did.Parse() should url-decode the components of a DID prior to applying constraints on the character space as defined by the generic DID syntax (which is the same as the URI syntax).

References:

• Generic DID Syntax: https://www.w3.org/TR/did-core/#did-syntax
• Generic URI Syntax: https://tools.ietf.org/html/rfc3986
  • Percent-encoding: https://tools.ietf.org/html/rfc3986#section-2.1
  • Reserved characters: https://tools.ietf.org/html/rfc3986#section-2.2
  • Unreserved characters: https://tools.ietf.org/html/rfc3986#section-2.3
  • When to encode or decode: https://tools.ietf.org/html/rfc3986#section-2.4
• URI recommendations: https://www.w3.org/Addressing/URL/4_URI_Recommentations.html
• Percent-encoded URI test vectors: https://www.w3.org/2004/04/uri-rel-test.html#reg-percent