fix(GlPagination): Fix extra space between span and icon

What does this MR do?

Closes #1021 (closed). Adds gl-display-flex to the Next and Prev buttons to remove the extra added white-space on the inner text span element. The current implementation does not match the design spec in Figma.

There are a number of ways to do this, but felt adding the gl-display-flex would be the simplest solution. However, I'm open to other solutions as well.

Screenshots

Before	After

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Closes #1021 (closed)