[Docs] unify scrim opacity

[manabu-nakamura]

Description: #3635

• https://m3.material.io/styles/elevation/applying-elevation:

Scrims use the scrim color role at an opacity of 32%.

• https://m3.material.io/components/navigation-drawer/specs:

Navigation drawers scrim color		md.ref.palette.neutral-variant20
Navigation drawers scrim opacity	0.4

• https://github.com/material-components/material-components-android/blob/master/docs/components/NavigationDrawer.md:

Element | Attribute | Related method(s)             | Default value
Color   | N/A       | setScrimColor on DrawerLayout | Black at 60% opacity

• https://m3.material.io/components/bottom-sheets/specs:

On Android platforms, the scrim color and opacity is automatically handled by the system UI.

Expected behavior:

• https://m3.material.io/styles/elevation/applying-elevation:
  No change.

Scrims use the scrim color role at an opacity of 32%.

• https://m3.material.io/components/navigation-drawer/specs:
  md.ref.palette.neutral-variant20 -> md.ref.palette.neutral-variant0 (BLACK)?
  0.4 -> 0.32

Navigation drawers scrim color		md.ref.palette.neutral-variant0
Navigation drawers scrim opacity	0.32

• https://github.com/material-components/material-components-android/blob/master/docs/components/NavigationDrawer.md:
  60% -> 32%

Element | Attribute | Related method(s)             | Default value
Color   | N/A       | setScrimColor on DrawerLayout | Black at 32% opacity

• https://m3.material.io/components/bottom-sheets/specs:
  Remove or revise the description (at least, the scrim opacity can be changed (f3e4439)).

On Android platforms, the scrim color and opacity is automatically handled by the system UI.

[manabu-nakamura]

#4530