Compute retaining paths for object

This CL adds a method getRetainingPaths to HeapSnapshotProxy. This
method finds the paths from an object to the GC roots. Unlike the
auto-expansion logic in the DevTools UI, it tries to find more than
one path to the root. Finding all retaining paths can be useful to
better understand from where the target object is kept alive.

getRetainingPaths() performs a DFS search starting from a target node
to the GC roots. For this it follows retainer edges of an object
sorted by the precomputed distance field of each retaining object.

The algorithm enforces limits on the recursion depth and the maximum
number of nodes/siblings to visit. getRetainingPaths() also returns
whether a limit (and which one) was reached during visitation.

Bug: 497855658
Change-Id: Ifa3fbadfddee7e2c1e4d98e008014bef0e97252a
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/7879915
Reviewed-by: Nikolay Vitkov <nvitkov@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Reviewed-by: Simon Zünd <szuend@chromium.org>