Issue Supporting Emojis in Full Text Search on Ubuntu

We rely on the Postgres tsvector implementation to enable full text search
in our app, but we're having some issues with getting the parser to
recognize emoji characters (like "😀" <U+1F600>) as anything other than
"blank"/"Space symbols" on Ubuntu per ts_debug(). Notably the characters
are recognized as "word"/"Word, all letters" characters on Mac; and
non-english, non-emoji characters (like "我" <U+6211>) are recognized as
"word" characters on both Mac and Ubuntu.

We greatly appreciate your feedback, debug details below and happy to
provide more as requested,
Jordan
pulsasensors.com, jhurwich@

Platform:
- AWS Ubuntu 18.04.2 LTS vs MacOS 10.15.5
- postgres (PostgreSQL) 11.5

* ts_debug() differs on MacOS and Ubuntu *

We have not modified the 'english' text search configuration on either
instance, however the query "SELECT * FROM ts_debug('english', '😀');"
returns different results on MacOS 10.15.5 and our Ubuntu instance:
- on MacOS:
db=# select * from ts_debug('english', '😀');
alias | description | token | dictionaries | dictionary |
lexemes
-------+-------------------+-------+----------------+--------------+---------
word | Word, all letters | 😀 | {english_stem} | english_stem | {😀}

- on Ubuntu:
db=# SELECT * from ts_debug('english','😀');
alias | description | token | dictionaries | dictionary | lexemes
-------+---------------+-------+--------------+------------+---------
blank | Space symbols | 😀 | {} | |

Notably non-english, non-emoji characters like '我' behave as desired on
both instances, with the same result on both MacOS and Ubuntu for "SELECT *
FROM ts_debug('english', '我');":
db=# SELECT * FROM ts_debug('english', '我');
alias | description | token | dictionaries | dictionary |
lexemes
-------+-------------------+-------+----------------+--------------+---------
word | Word, all letters | 我 | {english_stem} | english_stem | {我}

* pg_database *

There are minor differences between MacOS and Ubuntu in pg_database as
follows, however modifications to set datcollate and datctype to 'C' on
Ubuntu or the more specific 'en_US.UTF-8' have not changed the result for
ts_debug(). See row for 'testdb01':
- on Mac:
db=# select datname, encoding, datcollate, datctype, datistemplate from
pg_database;
datname | encoding | datcollate | datctype | datistemplate
----------------+----------+------------+----------+---------------
postgres | 6 | C | C | f
template0 | 6 | C | C | t
template1 | 6 | C | C | t
testdb01 | 6 | C | C | f

- on Ubuntu:
db=# select datname, encoding, datcollate, datctype, datistemplate from
pg_database;
datname | encoding | datcollate | datctype | datistemplate
-----------+----------+-------------+-------------+---------------
postgres | 6 | C.UTF-8 | C.UTF-8 | f
template0 | 6 | C.UTF-8 | C.UTF-8 | t
template1 | 6 | en_US.UTF-8 | en_US.UTF-8 | t
testdb01 | 6 | en_US.UTF-8 | en_US.UTF-8 | f

* locale *

The result of `$ locale` on both instances is similar, included below for
Ubuntu. Though `$ locale -a` varies considerably, on MacOS dozens of items
are returned while only 4 entries are returned on Ubuntu, included below:

- on Ubuntu
$ locale
LANG=en_US.UTF-8
LANGUAGE=
LC_CTYPE="en_US.UTF-8"
LC_NUMERIC="en_US.UTF-8"
LC_TIME="en_US.UTF-8"
LC_COLLATE="en_US.UTF-8"
LC_MONETARY="en_US.UTF-8"
LC_MESSAGES="en_US.UTF-8"
LC_PAPER="en_US.UTF-8"
LC_NAME="en_US.UTF-8"
LC_ADDRESS="en_US.UTF-8"
LC_TELEPHONE="en_US.UTF-8"
LC_MEASUREMENT="en_US.UTF-8"
LC_IDENTIFICATION="en_US.UTF-8"
LC_ALL=

- on Ubuntu
$ locale -a
C
C.UTF-8
en_US.utf8
POSIX

* Postgres installation *

On Mac, Postgres was installed and is managed by Homebrew via the
"postgresql(at)11" formula.
On Ubuntu, Postgres was installed from source at
https://ftp.postgresql.org/pub/source/v11.5/postgresql-11.5.tar.bz2.