fix(menu): support dark themes and non-grey backgrounds

[clshortfuse]

Menu popups should always be lightly colored and its content
should use their respective contrast color and opactiy.

• Set background color to background-100
• Use contrast values for buttons, icons, and dividers

Fixes #9100

[clshortfuse]

Blocked by PR #8872 #11376

[EladBezalel]

@clshortfuse i'm not sure it's correct by the material design spec,
please take a look at #5744

[clshortfuse]

@EladBezalel I see. Strange because that's not how Android's implementation of Material works.

Still, there is an issue because it's not using the right contrast values causing issues if you use anything other than gray. I'll update it to be lighter but still support changing backgroundPalette.

[clshortfuse]

Changed to hue-100 per spec. Now backgrounds properly render regardless of background palette.

Before:

After:

Dark:

[EladBezalel]

@clshortfuse dropdown menus should always be white:

[clshortfuse]

@EladBezalel

I took a colorpicker against the dropdown menu and it's not white. It's #FAFAFA which is actually grey-50. I'm using background-100 in the current screenshots above, so background-50 should keep it all to spec. It'll partially tint based on background color if users change backgroundPalette.

What it looks like now:

Light:

Dark:

If we want to hardcode the colors (#FAFAFA), it'll create some complications if the user decides to change the foreground color and/or use a dark theme. Perhaps we can add support in mdTheme for referencing by palette name, for example {{grey-50-background-contrast}}. As far as I can tell, that would be the safest solution.

[clshortfuse]

@EladBezalel can you take a look at it now that I switched to background-50. Or wait for the other PR, not sure how we should approach reviewing this.

[EladBezalel]

So i'm really not sure what we should assume about background colors..
I'm also not sure if even you have different background color you'd like background-50 and not #fafafa..

If we had a clear spec that said background-50 than I wouldn't be afraid it may break some people, maybe we want to postpone it to 1.2 ? i'm not really sure, it's a hard one!

[Splaktar]

This PR gives the following behavior (after rebasing, see this branch)

After we made a bunch of dark theme updates, 1.1.20 now gives this behavior

We're going to stick with the current behavior in 1.1.20 as it better aligns with our expectations of dark mode.