In SwissTable, don't hash the key when capacity<=1 on insertions.

This is applying SOO-like hashing behavior for small non-SOO-enabled tables.

Note that now we don't use the control bytes for capacity==1 tables, but we still allocate them. I left not allocating the control bytes in such cases as a followup.

PiperOrigin-RevId: 758373480
Change-Id: I152b313b7d770eb10fd6d175b5d9a07801274436

Author: ezbr