In defense against attack, assume the imported public key is not trusted
and check it matches the private key if set.
Added APIs that allow application to explicitly trust public key.
Original APIs default to not trusting public key.
* Added PK callback context tests for client/server examples (`SetupPkCallbackContexts`).
* Added new test define for `TEST_PK_PRIVKEY` to allows simulating hardware based private key.
* Added new test.h function for loading PEM key file and converting to DER (`load_key_file`).
* Added way to get private key signature size (`GetPrivateKeySigSize`).
* Added new ECC API `wc_ecc_sig_size_calc` to return max signature size for a key size.
* Added inline comments to help track down handshake message types.
* Cleanup of RSS PSS terminating byte (0xbc) to use enum value.
* Fixed bug with PK callback for `myEccVerify` public key format.
* Fixed bug with PK callback for ED25519 verify key buffer in DoServerKeyExchange.