[ncp] rename ControllerOpenThread to RcpHost

[Irving-cl]

This PR does a few renaming for ControllerOpenThread:

1. Rename file ncp_openthread.* to rcp_host.*
2. Rename all the member variable mNcp to mHost and all the
   parameters aNcp to aHost.
3. Rename the class ControllerOpenThread to RcpHost.

Currently the ControllerOpenThread actually works under RCP mode.
So the name Ncp is very confusing. RcpHost is used
in this PR so that we can later add NcpHost.

This PR is a subset of PR #2283 and only does some renaming.

[zhanglongxia]

LGTM

[codecov]

Codecov Report

Attention: Patch coverage is 40.25974% with 92 lines in your changes are missing coverage. Please review.

Project coverage is 39.76%. Comparing base (2b41187) to head (35a1c35).
Report is 665 commits behind head on main.

Files	Patch %	Lines
src/dbus/server/dbus_thread_object.cpp	9.09%	70 Missing ⚠️
src/border_agent/border_agent.cpp	53.84%	6 Missing ⚠️
src/sdp_proxy/discovery_proxy.cpp	33.33%	6 Missing ⚠️
src/ncp/rcp_host.cpp	81.81%	4 Missing ⚠️
src/trel_dnssd/trel_dnssd.cpp	40.00%	3 Missing ⚠️
src/rest/resource.cpp	60.00%	2 Missing ⚠️
src/utils/thread_helper.cpp	66.66%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2294       +/-   ##
===========================================
- Coverage   55.77%   39.76%   -16.01%     
===========================================
  Files          87       88        +1     
  Lines        6890     9779     +2889     
  Branches        0      721      +721     
===========================================
+ Hits         3843     3889       +46     
- Misses       3047     5692     +2645     
- Partials        0      198      +198     

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[superwhd]

LGTM 👍