[host] add SetThreadEnabled to ThreadHost APIs

[Irving-cl]

This PR adds a new method SetThreadEnabled as a ThreadHost API.

The method is added so that the Android binder API can be easily implemented without the need to handle NCP/RCP case. In this PR, RcpHost::SetThreadEnabled is impelmented and NcpHost::SetThreadEnabled will be implemented later.

[codecov]

Codecov Report

Attention: Patch coverage is 3.33333% with 29 lines in your changes missing coverage. Please review.

Project coverage is 45.67%. Comparing base (2b41187) to head (a075af5).
Report is 828 commits behind head on main.

Files with missing lines	Patch %	Lines
src/ncp/rcp_host.cpp	4.00%	24 Missing ⚠️
src/ncp/rcp_host.hpp	0.00%	3 Missing ⚠️
src/ncp/ncp_host.cpp	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2542       +/-   ##
===========================================
- Coverage   55.77%   45.67%   -10.10%     
===========================================
  Files          87      102       +15     
  Lines        6890    12100     +5210     
  Branches        0      887      +887     
===========================================
+ Hits         3843     5527     +1684     
- Misses       3047     6273     +3226     
- Partials        0      300      +300     

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[abtink]

LGTM. One smaller suggestion below:

[sunytt]

LGTM, thanks!