Update 6312-MUI6 showcase

[JeffGreiner-eaton]

Fixes # .
I was going to suggest some changes in #177 but seemed better to just open new PR to merge in to #177 .

Changes proposed in this Pull Request:

• temporary fix so we can build, test, lint & deploy

• updated DOMAttributes {
  component?: string | undefined;
  disabled?: string | undefined;
  selected?: string | undefined;

• updated <ListItem button> to <ListItemButton>

• updated <Divider light /> to <Divider sx={{ opacity: 0.6 }} />

• updated forwardRef on Alert

• updated datePicker to use slotProps={{ textField: { variant: 'outlined' } }}

Screenshots / Screen Recording (if applicable)

To Test:

• clone and build https://github.com/etn-ccis/blui-react-themes
• copy theme dist content over to showcase modules
• yarn lint && yarn prettier && yarn test && yarn build && yarn preview

Any specific feedback you are looking for?

[github-actions]

Visit the preview URL for this PR (updated for commit 3151819):

https://blui-react-showcase--pr178-feat-update-showcase-ybo0ug04.web.app

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