pgsql: libpq: Move cancellation related functions to fe-cancel.c

libpq: Move cancellation related functions to fe-cancel.c

In follow up commits we'll add more functions related to query
cancellations.  This groups those all together instead of mixing them
with the other functions in fe-connect.c.

The formerly static parse_int_param() function had to be exported to
other libpq users, so it's been renamed pqParseIntParam() and moved to a
more reasonable place within fe-connect.c (rather than randomly between
various keepalive-related routines).

Author: Jelte Fennema-Nio <jelte.fennema@microsoft.com>
Discussion: https://postgr.es/m/AM5PR83MB0178D3B31CA1B6EC4A8ECC42F7529@AM5PR83MB0178.EURPRD83.prod.outlook.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/6d4565a05f3fb9b7a439e7ecfc2be68bf4dabf48

Modified Files
--------------
src/interfaces/libpq/Makefile     |   1 +
src/interfaces/libpq/fe-cancel.c  | 387 ++++++++++++++++++++++++++++++
src/interfaces/libpq/fe-connect.c | 483 +++++---------------------------------
src/interfaces/libpq/libpq-int.h  |   5 +
src/interfaces/libpq/meson.build  |   1 +
5 files changed, 451 insertions(+), 426 deletions(-)