.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 <[email protected]>
Cc: Laszlo Ersek <[email protected]>
Cc: Leif Lindholm <[email protected]>
Signed-off-by: Kinney <[email protected]>
Reviewed-by: Leif Lindholm <[email protected]>
Reviewed-by: Philippe Mathieu-Daude <[email protected]>
Reviewed-by: Laszlo Ersek <[email protected]>
Reviewed-by: Liming Gao <[email protected]>

.gitignore

@@ -1,3 +1,7 @@
 Build/
-tags/
 .DS_Store
+*_extdep/
+*.pyc
+__pycache__/
+tags/
+.vscode/