Add [iSelect], and various tactics based on it

This MR adds the following tactics:

• iSelect (pat)%I tac calls the tactic tac with the name of the last hypothesis of the Iris context matching pat,
• iRename select (pat)%I into name renames the last hypothesis of the Iris context matching pat into name,
• iDestruct select (pat)%I as ... is similar to iDestruct but it acts on the last hypothesis of the Iris context matching pat,
• iClear select (pat)%I clears the last hypothesis of the Iris context matching pat,
• iRevert select (pat)%I reverts the last hypothesis of the Iris context matching pat,
• iFrame select (pat)%I cancels the last hypothesis of the Iris context matching pat.