pgsql: Convert uses of hash_string_pointer to fasthash equivalent

Convert uses of hash_string_pointer to fasthash equivalent

Remove duplicate hash_string_pointer() function definitions by creating
a new inline function hash_string() for this purpose.

This has the added advantage of avoiding strlen() calls when doing hash
lookup. It's not clear how many of these are perfomance-sensitive
enough to benefit from that, but the simplification is worth it on
its own.

Reviewed by Jeff Davis

Discussion: https://postgr.es/m/CANWCAZbg_XeSeY0a_PqWmWqeRATvzTzUNYRLeT%2Bbzs%2BYQdC92g%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/f956ecd0353b2960f8322b2211142113fe2b6f67

Modified Files
--------------
src/bin/pg_combinebackup/load_manifest.c | 16 ++--------------
src/bin/pg_dump/pg_dumpall.c | 17 ++---------------
src/bin/pg_rewind/filemap.c | 17 ++---------------
src/bin/pg_verifybackup/pg_verifybackup.c | 16 ++--------------
src/include/common/hashfn_unstable.h | 20 ++++++++++++++++++++
5 files changed, 28 insertions(+), 58 deletions(-)