[foreign-memaccess+abi] RFR: Simplify code now that bitSize is always aligned to byte boundaries [v2]

[Maurizio Cimadamore]

On Thu, 16 Feb 2023 13:59:21 GMT, Per Minborg <pminborg at openjdk.org> wrote:

>> This PR suggests some simplifications now that layouts are always aligned to byte boundaries. 
>> 
>> The PR also contains some other simplifications/cleanups.
>
> Per Minborg has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Update after comments

Marked as reviewed by mcimadamore (Committer).

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PR: https://git.openjdk.org/panama-foreign/pull/796