BIND 10 #2498: support generic version of rdata::createRdata(text) in HINFO and NAPTR

[BIND 10 Development]

#2498: support generic version of rdata::createRdata(text) in HINFO and NAPTR
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            Reporter:  jinmei        |                        Owner:
                Type:  task          |  UnAssigned
            Priority:  medium        |                       Status:  new
           Component:  libdns++      |                    Milestone:  New
           Sensitive:  0             |  Tasks
         Sub-Project:  DNS           |                     Keywords:
Estimated Difficulty:  0             |              Defect Severity:  N/A
         Total Hours:  0             |  Feature Depending on Ticket:
                                     |  loadzone-ng
                                     |          Add Hours to Ticket:  0
                                     |                    Internal?:  0
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 Subtask of #2368, depend on #2374.

 See #2382.

 Also see #2442.  We should use the helper `strToCharstring()`
 function.  Also the internal data type for char-string should be
 changed to `CharString` (std::string is not appropriate as char-string
 can contain 8-bit values larger than 127).

 Once implemented, update the hardcode list introduced in
 #2497.

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Ticket URL: <https://bind10.isc.org/ticket/2498>
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