CodeViewer/CodeEditor: Add support for highlighting specific lines

[lottamus]

User story.

As a @stoplight/ui-kit user, I can pass a prop to the CodeViewer and CodeEditor components, so that I can highlight specific code lines.

Describe the solution you'd like

Update the following to take an optional "highlightLines" prop:

• CodeEditor component: https://github.com/stoplightio/ui-kit/blob/master/src/CodeEditor/index.tsx#L10
• CodeViewer component: https://github.com/stoplightio/ui-kit/blob/master/src/CodeViewer/index.tsx#L15
• highlightCode util function: https://github.com/stoplightio/ui-kit/blob/master/src/CodeEditor/utils/highlightCode.ts#L30

Additional context

The highlightLines prop should have the following typing:

type highlightLines = [number, number?] | Array<[number, number?]>;

Examples:

// The following will highlight lines 1, 2, and 3
<CodeViewer language={language} value={code} highlightLines={[1, 3]} />

// The following will highlight lines 1, 3, 4, and 5
<CodeViewer language={language} value={code} highlightLines={[[1], [3, 5]]} />