Use scatter api in fips mode

[toidiu]

Problem:

We enabled fips crypto in PR by using the aws-lc-rs type TlsRecordSealingKey.seal_in_place_separate_tag.

In non-fips mode we use LessSafeKey.seal_in_place_scatter which resulted in an 8% efficiency gain. We should work with aws-lc-rs to add the scatter encrypt call to the TlsRecordSealingKey struct