[memprof] Use CallStackRadixTreeBuilder in the V3 format (#94708)

This patch integrates CallStackRadixTreeBuilder into the V3 format,
reducing the profile size to about 27% of the V2 profile size.

- Serialization: writeMemProfCallStackArray just needs to write out
  the radix tree array prepared by CallStackRadixTreeBuilder.
  Mappings from CallStackIds to LinearCallStackIds are moved by new
  function CallStackRadixTreeBuilder::takeCallStackPos.

- Deserialization: Deserializing a call stack is the same as
  deserializing an array encoded in the obvious manner -- the length
  followed by the payload, except that we need to follow a pointer to
  the parent to take advantage of common prefixes once in a while.
  This patch teaches LinearCallStackIdConverter to how to handle those
  pointers.