pgsql: Add mbverifystr() functions specific to each encoding.

Add mbverifystr() functions specific to each encoding.

This makes pg_verify_mbstr() function faster, by allowing more efficient
encoding-specific implementations. All the implementations included in
this commit are pretty naive, they just call the same encoding-specific
verifychar functions that were used previously, but that already gives a
performance boost because the tight character-at-a-time loop is simpler.

Reviewed-by: John Naylor
Discussion: https://www.postgresql.org/message-id/e7861509-3960-538a-9025-b75a61188e01@iki.fi

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/b80e10638e36b9d2f0b39170c613837af2ca2aac

Modified Files
--------------
src/backend/commands/extension.c | 2 +-
src/backend/utils/mb/conv.c | 2 +-
.../euc2004_sjis2004/euc2004_sjis2004.c | 4 +-
.../euc_jp_and_sjis/euc_jp_and_sjis.c | 10 +-
.../euc_kr_and_mic/euc_kr_and_mic.c | 4 +-
.../euc_tw_and_big5/euc_tw_and_big5.c | 8 +-
src/backend/utils/mb/mbutils.c | 31 +-
src/common/wchar.c | 523 ++++++++++++++++++---
src/include/mb/pg_wchar.h | 10 +-
9 files changed, 493 insertions(+), 101 deletions(-)