Users of the nvs API are likely to have `nvs_handle_t` in all cases, but
not all of them carry around the partition name and namespace name (as
they aren't needed after creating an `nvs_handle_t`).
Allow this common case to use nvs iteration without them tracking
additional data by using the `nvs_handle_t` to locate the namespace
index and the partition name by introducing an alterate to
`nvs_entry_find` called `nvs_entry_find_in_handle`, which operates
similarly except that it is given a `nvs_handle_t` instead of partition
and namespace strings.
This is somewhat more limited than the `nvs_entry_find` API as one
cannot examine all keys in a given partition.
With some libc impls (ie: Xcode 13.1), sprintf is marked as deprecated
and causes the build with `-Werror` to fail. Switch the `sprintf` usage
in test_nvs.cpp to use `snprintf` to allow builds to complete without
warning.
Host tests of nvs_flash eligible to run in Linux implementation of nvs flash were migrated. Remaining test cases
were left in original folder. Migrated test cases use CMake instead of make.
