s/pg_attribute_always_inline/pg_always_inline/?

Hi,

When reviewing the index prefetching patch I got a bit dismayed at how long
pg_attribute_always_inline is due to the way it triggers pgindent to format
stuff.

I propose that we remove the _attribute_ part of the name.

Given that it is implemented for compilers that don't use the
__attribute__((always_inline)) spelling, so the shorter name seems better
anyway.

Thoughts?

Greetings,

Andres Freund