Add reopen action to closed MR widget state

A follow-up on MR Merge Widget new Framework: Update merged, c... (#368039 - closed)

🖼 Design specs in Figma

Summary of the changes

1. Add Reopen action to the MR widget state, the action should support responsive design

Design-generated CSS

Note that this is Figma CSS, so may not have any applicability in the GitLab product.

/* Label */

width: 49px;
height: 16px;

/* UI/Label/Regular */
font-family: 'Helvetica Neue';
font-style: normal;
font-weight: 400;
font-size: 14px;
line-height: 16px;

/* identical to box height, or 114% */
display: flex;
align-items: center;

/* Blue/$blue-500 :: #1F75CB */
color: #1F75CB;


/* Inside auto layout */
flex: none;
order: 0;
flex-grow: 0;