[TextField] Fix FilledInput AA contrast issue

[Dripcoding]

Update opacity for light backgroundColor in FilledInput
Update opacity in palette

Fixes #249247

• I have followed (at least) the PR section of the contributing guide.

[mui-pr-bot]

Details of bundle changes

Generated by 🚫 dangerJS against eb03da1

[oliviertassinari]

Many of the changes are within the approximation threshold of Argos-CI (not reporting changes). Here is an example:

before

after

I can't think of any concern, it looks like a great change.

[eps1lon]

I don't think we should change the palette as a whole. If there's a problem with the TextField -> just change the TextField. If there's a problem with the palette -> show the problem with the palette. If that problem only exists with the TextField, don't change the palette since that can have unintended side-effects.

[oliviertassinari]

If there's a problem with the palette -> show the problem with the palette

@eps1lon

https://material.io/design/color/text-legibility.html#text-backgrounds

[oliviertassinari]

@Dripcoding What do you think about splitting the change into two pull requests? The first one to update the palette, to get a proper entry in the changelog, and this one to polish the filled text field?

[Dripcoding]

@oliviertassinari I think splitting this PR makes sense so that each addresses a different issue. I'll split this PR once I get off work today. Also should I create a separate issue for the palette change?

[oliviertassinari]

Also should I create a separate issue for the palette change?

I don't think so, I think that detailing the motivation for the change is enough.

[Dripcoding]

@oliviertassinari @eps1lon I've split this PR with this for the FilledInput.

#25060 is for changing the palette.

[eps1lon]

Now I get it. Thanks for taking the time explaining both issues!

[oliviertassinari]

@Dripcoding Perfect, a better aesthetic and a11y (I only hope the background is dark enough to be seen)