Find places where uno::Sequence is passed by value.

Implement a clang plugin to find them, and clean up existing code
to pass them by reference.

Change-Id: If642d87407c73346d9c0164b9fc77c5c3c4354b8
Reviewed-on: https://gerrit.libreoffice.org/9351
Reviewed-by: Noel Grandin <noelgrandin@gmail.com>
Tested-by: Noel Grandin <noelgrandin@gmail.com>