This commit adds a method `Dataset::IsSubsetOf()` to check whether one
dataset is a subset of another. A dataset is considered a subset if
all its TLVs, excluding Active/Pending Timestamp and Delay Timer
TLVs, are present in the other dataset with exactly matching values.
This new method simplifies `Dataset::Info::IsSubsetOf()`. The unit
test `test_dataset` is updated to validate the `IsSubsetOf()()`
method.
This commit enhances dataset handling:
- Adds `ValidateTlvs()` which parses and validates all known TLVs
within the `Dataset` and checks for any duplicates.
- Introduces a set of `SetFrom()` methods for constructing a `Dataset`
from various types of inputs, e.g., other `Dataset`, TLV sequences,
`DatasetInfo` structures, bytes read from `Message`. Now they
consistently clear the `Dataset` before setting it.
- Adds `WriteTlvsFrom()` to update a `Dataset` replacing/appending a
set of TLVs.
- Adds `AppendTlvsFrom()` to append an already encoded sequence of
TLVs without validating/checking the format.
- Renames `Get/SetSize()` to `Get/SetLength()` for consistency.
- Adds `test_dataset.cpp` unit test for basic `Dataset` validation.
Abtin Keshavarzian