Change destructive foreground color

[JMalheiros]

Related to issue Destructive button preview in docs has red text over red background #252

Changed destructive-foreground color to white. It contrasts better with the red from the background.
This constant is used on both Link and Button component, so changed for both of them.
Note: there are two commits on this PR:

• First one changes the destructive-foreground color so we have contrast on both light and dark modes.
• Second one, changes the destructive color to a red a little darker. By WCAG2 patterns, the contrast between white and the older red is not perfectly contrastable to the AAA levels. This one is just a suggestion, and can be reverted easily.

WCAG2 comparison between original destructive and destructive-foreground colors:

WCAG2 comparison between slight darker destructive and destructive-foreground colors:

Button and Link with original destructive and destructive-foreground colors:

Button and Link with slight darker destructive and destructive-foreground colors: