[Mac/iOS/GN] Allow targets to override the output directory.

This uses the new output_dir override of GN (see
https://codereview.chromium.org/1887533003) in the tool definitions to allow
targets to override this location.

Updates the framework_bundle() template to specify an output_dir as well.

[email protected]
BUG=297668

Review URL: https://codereview.chromium.org/1886813003

Cr-Commit-Position: refs/heads/master@{#387464}
2 files changed