**Problem**
`ITheme.getColor` is one of the major users of the type `null` in our codebase. However this function is used in many places that expected an `undefined` type instead. With the strict null work, this means that we have to write code such as `theme.getColor(...) || undefined` in some cases or have to work with  `Color | null | undefined` types.

**Fix**
`undefined` is generally better supported by TypeScript and more natural in JavaScript. This change makes `ITheme.getColor` return `Color | undefined` instead of `Color | null`.

fixes #67918

fixes #67446

separate schema for workbenchColors and textmateColors, to avoid repetition in configuration schemas

[loc] The phrase 'The color must not be opaque to not hide underlying decorations' is incorrect. Fixes #66333

The sentence 'The color must not be opaque to not hide underlying
decorations' is incorrect. This PR replaces 'to not hide' with
'so as not to hide'. See the link below for why:
https://english.stackexchange.com/questions/45265/use-of-so-as-not-to

Closes #66333

We compile using the alwaysStrict flag so these directives are not needed

This part removes most `use strict` directives that are right after the file header

* refactor menu theming to be cleaner and remove css colors

* add separator color back

* remove dynamic css, inline styles only

* remove bg color

* add option for input validation foreground color for findWidget

* fix copy paste mistakes

* removing defaults for foreground color

* add inputValidationForeground wherever inputValidationBackground is used

* add inputValidationForeground color