[lldb/Core] Change large function threshold variable into a setting.

This patch replaces the static large function threshold variable with a
global debugger setting (`stop-disassembly-max-size`).

The default threshold is now set to 32KB (instead of 8KB) and can be modified.

rdar://74726362

Differential Revision: https://reviews.llvm.org/D97486



Signed-off-by: Med Ismail Bennani <medismail.bennani@gmail.com>