rustdoc: add ways of collapsing all impl blocks

either shift+click the Summary button,
or use the `_` key.

this collapses everything,
including (inherent) impl blocks.

no need for a special "expand all impl blocks"
method, as impl blocks are expanded during regular
"expand all".
doing "expand all" -> "collapse all" will always
result in only impl blocks being expaned.

some of the html is split up a bit awkwardly to
try to avoid introducing new whitespaces nodes,
which could affect display.

Co-authored-by: Guillaume Gomez <guillaume1.gomez@gmail.com>

0 files changed, 0 insertions, 0 deletions