utils: Add debugging script for lsif-clang failures.

[varungandhi-src]

This script slices up a compile_commands.json into multiple json files, and runs lsif-clang separately for each file.

# Fail fast (exit after first error), prints Clang error output and reproduction information
./utils/lsif-clang-driver.py /path/to/lsif-clang /path/to/compile_commands.json

Found lsif-clang failure (stdout+stderr below):
--------------------------------------------------------------
[1/1] Processing file /Users/varun/Code/lsif-clang/clang-tools-extra/clangd/FS.cpp
In file included from /Users/varun/Code/lsif-clang/clang-tools-extra/clangd/FS.cpp:9:
<snipped>
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX12.3.sdk/usr/include/wchar.h:89:10: fatal error: 'stdarg.h' file not found
#include <stdarg.h>
         ^~~~~~~~~~
1 error generated.
Error while processing /Users/varun/Code/lsif-clang/clang-tools-extra/clangd/FS.cpp.
--------------------------------------------------------------

Reproduce the failure by running:
  /Users/varun/Code/lsif-clang/bin/lsif-clang /var/folders/tr/gylnxkts3bn0gyhhlrv8z9_m0000gn/T/tmps5sae_qm-repro/compile_commands.json

# Don't fail fast, printing all output and showing the number of errors at the end
./utils/lsif-clang-driver.py /path/to/lsif-clang /path/to/compile_commands.json --no-fail-fast

<snipped>
Reproduce the failure by running:
  /Users/varun/Code/lsif-clang/bin/lsif-clang /var/folders/tr/gylnxkts3bn0gyhhlrv8z9_m0000gn/T/tmpb30_2b8a-repro/compile_commands.json

30/31 lsif-clang commands failed. 😭

There are also other flags to suppress the Clang output (the reproduction instructions will still be printed) and to control the level of concurrency (defaults to number of CPUs). (See --help.)

Test plan

Manually tested.