The user can switch to the main <summary> by tab key, and toggle the
<details> by either 'space' key or 'enter' key.
'return' key is handled with 'keypress', and the 'space' key is handled
with 'keyup' like the HTMLInputElement.
MozReview-Commit-ID: HE6IduUGCpj
--HG--
extra : rebase_source : 34598d95f35bf6b5bd927457ee09e42eb6ec0a68
Ting-Yu Lin