[code snippet] single line and multi-line bugs

There are a couple different bugs with the single line and multi-line code snippets.

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Single line:

• The active state is not showing up when clicking on the copy button. It should be active-ui on click.

• The horizontal scroll does not have a fade style. (This may be resolved with Andrews fix for horizontal tab scrolling.)

• When the light prop is active, the dark themes have incorrect hover states for the copy button and show more button. They should be using hover-light-ui for hover. (this is also happening for inline code snippet)

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Multi-line:

• The active state is not showing up when clicking on the copy button (same problem with single line above^).
• When the light prop is active, the dark themes have incorrect hover states for the copy button and show more button. They should be using hover-light-ui for hover.
• The copy button should have a 8px top and right padding within the field background so that it vertically aligns with the chevron icon in the show more button below it.

[laurenmrice]

Overflow issue (horizontal scroll)

• The fade style should be the same as what we currently use for the modal component when a modal scrolls vertically.

Spec:

[laurenmrice]

Hover issue:

• The current values for the hover-light-ui token are correct. The color is not displaying correctly on hover for the dark themes.

Example of what is happening now:

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This is what it should look like: