Improve indentation of multiline initialization expressions.

Improve indentation of multiline initialization expressions.

If a variable has an initialization expression that wraps onto the
next line(s), pg_bsd_indent will now indent the continuation lines
one stop, instead of aligning them flush with the variable declaration.

We've been holding off applying this until the last v16 CF finished,
but now it's time.

Thomas Munro and Tom Lane

Discussion: https://postgr.es/m/20230120013137.7ky7nl4e4zjorrfa@awork3.anarazel.de