Use hierarchical Jump-to links

https://issues.dlang.org/show_bug.cgi?id=5136

Show only top-level symbols in the main module jump-to links, with remaining symbols shown in separate jump-to lists before their respective parents.

Show non-top-level jump-to links even when `inhibitQuickIndex` is set.
Show all jump-to links with same background color as symbol declarations.

Note: std.typecons and std.container.rbtree are nice modules to test this with.