pgsql: PL/Python: Refactor for event trigger support

PL/Python: Refactor for event trigger support

Change is_trigger type from boolean to enum.  That's a preparation for
adding event trigger support.

Author: Euler Taveira <euler@eulerto.com>
Co-authored-by: Dimitri Fontaine <dimitri@2ndQuadrant.fr>
Reviewed-by: Pavel Stehule <pavel.stehule@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/03f03515-2068-4f5b-b357-8fb540883c38%40app.fastmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/6e09c960ebb353c6cbcc05191c68aea4079df277

Modified Files
--------------
src/pl/plpython/plpy_exec.c      |  2 +-
src/pl/plpython/plpy_main.c      | 24 ++++++++++++++++++------
src/pl/plpython/plpy_procedure.c | 15 ++++++++++-----
src/pl/plpython/plpy_procedure.h | 13 +++++++++++--
src/tools/pgindent/typedefs.list |  1 +
5 files changed, 41 insertions(+), 14 deletions(-)