pgsql: Speed up lexing of long JSON strings

Speed up lexing of long JSON strings

Use optimized linear search when looking ahead for end quotes,
backslashes, and non-printable characters. This results in nearly 40%
faster JSON parsing on x86-64 when most values are long strings, and
all platforms should see some improvement.

Reviewed by Andres Freund and Nathan Bossart
Discussion:
https://www.postgresql.org/message-id/CAFBsxsGhaR2KQ5eisaK%3D6Vm60t%3DaxhD8Ckj1qFoCH1pktZi%2B2w%40mail.gmail.com
Discussion: https://www.postgresql.org/message-id/CAFBsxsESLUyJ5spfOSyPrOvKUEYYNqsBosue9SV1j8ecgNXSKA%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/0a8de93a48ce1e7479fb75fe10a8859559ec0c09

Modified Files
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src/common/jsonapi.c               | 13 ++++++++++---
src/test/regress/expected/json.out | 13 +++++++++++++
src/test/regress/sql/json.sql      |  5 +++++
3 files changed, 28 insertions(+), 3 deletions(-)