Fix lldb-vscode logging and enable logging for all lldb-vscode tests.

Summary:
This patch fixes logging to log incoming packets which was removed during a refactor.

We also enable logging to a "vscode.txt" file for each lldb-vscode test by creating the log file in the build artifacts directory for each test. This allows users to see the packets for their tests if needed and the log file is in a directory that will be removed after tests have been run.

Reviewers: labath, aadsm, serhiy.redko, jankratochvil, xiaobai, wallace

Subscribers: lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D74566