[host] add active dataset as a network property

[Irving-cl]

This PR adds active dataset tlvs to NetworkProperties so that for both NCP and RCP active dataset can be accessed directly.

The active dataset is used in many places in the platform code. For example, in android SetThreadEnabled, it will only enable Thread when the active dataset is a valid one.

I verified the NCP case locally by log (dumping the active set and see if it's correctly set). If writing a test for it, we need add one more dbus API, which seems unworthy now.

[codecov]

Codecov Report

Attention: Patch coverage is 4.16667% with 23 lines in your changes missing coverage. Please review.

Project coverage is 45.43%. Comparing base (2b41187) to head (2adfd2b).
Report is 829 commits behind head on main.

Files with missing lines	Patch %	Lines
src/ncp/ncp_spinel.cpp	0.00%	12 Missing ⚠️
src/ncp/ncp_host.cpp	14.28%	6 Missing ⚠️
src/ncp/rcp_host.cpp	0.00%	5 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2540       +/-   ##
===========================================
- Coverage   55.77%   45.43%   -10.35%     
===========================================
  Files          87      102       +15     
  Lines        6890    11995     +5105     
  Branches        0      877      +877     
===========================================
+ Hits         3843     5450     +1607     
- Misses       3047     6251     +3204     
- Partials        0      294      +294     

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[zhanglongxia]

LGTM

[abtink]

Looks great. 👍