InputControl and TextareaControl: label, placeholder, and background colors should work consistently and be always readable

Description

While going through https://github.com/WordPress/gutenberg/issues/60275, https://github.com/WordPress/gutenberg/pull/68807, https://github.com/WordPress/gutenberg/pull/69312, and https://github.com/WordPress/gutenberg/pull/69334, I noticed InputControl and TextareaControl hav einconsistent and buggy behaviors for:

• The label color.
• The placeholder attribute color.
• The input and textarea background color.
• The input and textarea background color when disabled.

This is more noticeable when using the components inside the editor canvas with both a light and dark backgrounds.

One of these buggy behaviors is surfaced after the is-dark-theme CSS class for the Post Editor was fixed in https://github.com/WordPress/gutenberg/pull/68481

I'd expect these two components to use a consistent styling for all states and have the same behavior with a dark background theme. Cc @WordPress/gutenberg-components

To quickly test, I added the components below to the PostTitle:

<TextareaControl
	label="TextareaControl"
	placeholder="Placeholder"
	rows={ 3 }
	__nextHasNoMarginBottom
/>
<br />
<InputControl
	__next40pxDefaultSize
	type="text"
	value=""
	label="InputControl"
	placeholder="Placeholder"
/>
<br />
<TextareaControl
	label="TextareaControl disabled"
	placeholder="Placeholder"
	rows={ 3 }
	__nextHasNoMarginBottom
	disabled
/>
<br />
<InputControl
	__next40pxDefaultSize
	type="text"
	value=""
	label="InputControl disabled"
	placeholder="Placeholder"
	disabled
/>
<br />

Light	Dark

Once the ongoing work on the placeholder text color in the issues linked above is c