[lldb/crashlog] Fix scripted_crashlog_json.test failure

[lldb/crashlog] Fix scripted_crashlog_json.test failure

This patch should fix the test failure on scripted_crashlog_json.test.

The failure is happening because crash reporter will obfuscate the
executable path in the crashlog, if it is located inside the user's
home directory and replace it with `/USER/*/` as a placeholder.

To fix that, we can patch the placeholder with the executable path
before loading the crashlog in lldb.

This also fixes a bug where we would create another target when loading
the crashlog in a scripted process, even if lldb already had a target
for it. Now, crashlog will only create a target if there is none in lldb.

Differential Revision: https://reviews.llvm.org/D120598

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