.gitignore: Ignore python compiled files, extdeps, and vscode

.gitignore: Ignore python compiled files, extdeps, and vscode

https://bugzilla.tianocore.org/show_bug.cgi?id=2315

Update .gitignore to ignore .pyc files and __pycache__
directories.  Python based plugins can be added to any
package or platform, so these files and directories may
be present outside of BaseTools.

Ignore _extdep directories that are generated by the
pytool external dependency feature.

Ignore .vscode directories generated by the VS Code
editor.

Cc: Andrew Fish <afish@apple.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Leif Lindholm <leif.lindholm@linaro.org>
Signed-off-by: Kinney <michael.d.kinney@intel.com>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
Reviewed-by: Philippe Mathieu-Daude <philmd@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>