Revert "[core] Remove outdated babel proposal plugins (#36795)"

[michaldudak]

This reverts #36795

Without the removed plugins, the code was not transpiled correctly for Safari 12.5, which we still support. We will update the supported browsers list with the next major release. Then, we'll be able to revisit that PR.

[mui-bot]

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@material-ui/core: parsed: +3.78% , gzip: +3.83%
@material-ui/lab: parsed: +2.94% , gzip: +3.03%
@material-ui/system: parsed: +1.39% , gzip: +1.23%
@material-ui/unstyled: parsed: +3.20% , gzip: +2.57%
@mui/material-next: parsed: +1.85% , gzip: +1.89%
@mui/joy: parsed: +2.76% , gzip: +2.75%

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[ZeeshanTamboli]

Okay, let's revert. I added it to the v6 milestone and in #30660.

I'm curious as to how may users still use Safari 12.5 on iOS. Perhaps it can be checked in Google Analytics if we are tracking it.

[michaldudak]

According to browserslist it's 0.62% globally (https://browsersl.ist/#q=ios_saf+%3C%3D+12.5), but we can't change support between majors.