Handle horizontal and vertical overflow for selected code snippet.

[mk-fan]

Issue #, if available:

• N/A

Description of changes: For selected code snippet

• When overflow horizontally, we will add ellipsis
• When overflow vertically, we will add a fading effect at the bottom

For preview overlay

• When overflow horizontally, we will add ellipsis

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[mk-fan]

Changes already included in https://github.com/aws/mynah-ui/commit/f500234f1baec1fa18935c08672ab7fb20946c4c. Close the PR.