Update buttons with icons wrapping style

[maureenlholland]

As noted in this PR comment: mozmeao/springfield#897 (comment)

Need to consult with design on what the ideal default behaviour would be when buttons with icons wrap. Confirm if this is a download-button-specific case or general use.

text wrap balance (keeping current inline-block display)

change to flex display, no shrink and center align on icon

...something else?

[janbrasna]

When this enhancement was added, I experimented with aligning it instead of wrapping: mozilla/bedrock#14483

[stephaniehobson]

Lets go with your second option "change to flex display, no shrink and center align on icon".