Add Primary/Secondary/Tertiary/QuaternaryContentStyle

[carson-katri]

These styles have 2 different behaviors:

1. Use the styles specified in a foregroundStyle modifier:

Group {
  Text("Primary").foregroundStyle(.primary)
  Text("Secondary").foregroundStyle(.secondary)
  Text("Tertiary").foregroundStyle(.tertiary)
  Text("Quaternary").foregroundStyle(.quaternary)
}
.foregroundStyle(.red, .green, .blue)

2. Use the foreground color and apply opacity:

Group {
  Text("Primary").foregroundStyle(.primary)
  Text("Secondary").foregroundStyle(.secondary)
  Text("Tertiary").foregroundStyle(.tertiary)
  Text("Quaternary").foregroundStyle(.quaternary)
}
.foregroundColor(.blue)

[MaxDesiatov]

Do we have a certainty that foregroundStyle.styles is always non-empty? If so, maybe this needs a comment in code to explain that?

Also, this PR needs conflicts to be resolved 🙂

[carson-katri]

I replaced the array with a tuple to guarantee its non-empty.

[MaxDesiatov]

Sweet! 🙌