[lldb] Increase the rate at which ConstString's memory allocator scales the...

[lldb] Increase the rate at which ConstString's memory allocator scales the memory chunks it allocates

Summary:
We currently do far more malloc calls than necessary in the ConstString BumpPtrAllocator. This is due to the 256 BumpPtrAllocators
our ConstString implementation uses internally which end up all just receiving a small share of the total allocated memory
and therefore keep allocating memory in small chunks for far too long. This patch fixes this by increasing the rate at which we increase the
memory chunk size so that our collection of BumpPtrAllocators behaves in total similar to a single BumpPtrAllocator.

Reviewers: llunak

Reviewed By: llunak

Subscribers: abidh, JDevlieghere, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D71699