[thread host] add ThreadHost Error code

[Irving-cl]

This PR adds ThreadHost error code and use it as part of the ThreadHost API.

Following openthread/openthread#10990, currently otErrors are used in ThreadHost APIs. But some specific errors in ThreadHost APIs cannot be denoted by otError and these errors do need to be differentiated by the client code. For example, kErrorThreadDisabled means some action is taken when Thread is 'Disabled' while 'Thread Disabled' is a concept for ThreadHost APIs and beyond the scope of openthread.

This PR adds ThreadHost error code which is a superset of otErrors and contains a few proprietary errors that could be used to represent some specific cases.

This PR also replaces the existing usage of otError in the client code of ThreadHost APIs.

[codecov]

Codecov Report

Attention: Patch coverage is 61.17647% with 33 lines in your changes missing coverage. Please review.

Project coverage is 45.86%. Comparing base (2b41187) to head (651fa7b).
Report is 891 commits behind head on main.

Files with missing lines	Patch %	Lines
tests/gtest/test_rcp_host_api.cpp	69.44%	22 Missing ⚠️
src/dbus/server/dbus_thread_object_ncp.cpp	0.00%	10 Missing ⚠️
src/ncp/rcp_host.cpp	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2633      +/-   ##
==========================================
- Coverage   55.77%   45.86%   -9.92%     
==========================================
  Files          87      106      +19     
  Lines        6890    12855    +5965     
  Branches        0      929     +929     
==========================================
+ Hits         3843     5896    +2053     
- Misses       3047     6636    +3589     
- Partials        0      323     +323     

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[abtink]

Thanks. LGTM 👍