pgsql: Rename StartBackgroundWorker() to BackgroundWorkerMain().

Rename StartBackgroundWorker() to BackgroundWorkerMain().

The comment claimed that it is "called from postmaster", but it is
actually called in the child process, pretty early in the process
initialization. I guess you could interpret "called from postmaster"
to mean that, but it seems wrong to me. Rename the function to be
consistent with other functions with similar role.

Reviewed-by: Thomas Munro
Discussion: https://www.postgresql.org/message-id/4f95c1fc-ad3c-7974-3a8c-6faa3931804c@iki.fi

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/637109d13ab2684aa7ad4e893137e7487b5e8490

Modified Files
--------------
src/backend/postmaster/bgworker.c           | 7 ++-----
src/backend/postmaster/postmaster.c         | 4 ++--
src/include/postmaster/bgworker_internals.h | 4 ++--
3 files changed, 6 insertions(+), 9 deletions(-)