Fix pointer truncation crash caused by missing get_database_name declaration

[bigplaice]

PostgreSQL commit 20abdc9e82 ("Avoid including commands/dbcommands.h in
so many places") moved the declaration of get_database_name() from
commands/dbcommands.h to utils/lsyscache.h. Extensions that relied on
the old header location no longer get a proper function prototype,
causing the compiler to assume the function returns int (32-bit) instead
of char * (64-bit). On x86_64 this silently truncates the returned
pointer, leading to a segmentation fault when the truncated pointer is
later dereferenced (e.g. by strlen inside snprintf).

Use utils/lsyscache.h on PostgreSQL 19+ where the declaration lives
there, and fall back to commands/dbcommands.h on older versions where it
is still provided.

[bigplaice]

Base code: postgresql-19beta1

In contrib directory,
wget https://github.com/amutu/zhparser/archive/refs/tags/v2.3.tar.gz
make PG_CONFIG=/home/highgo/pg/inst/bin/pg_config
make PG_CONFIG=/home/highgo/pg/inst/bin/pg_config install

When build source code, there is WARNING:
zhparser.c: In function ‘init’:
zhparser.c:85:13: warning: old-style function definition [-Wold-style-definition]
zhparser.c:216:34: warning: implicit declaration of function ‘get_database_name’; did you mean ‘GetDatabasePath’? [-Wimplicit-function-declaration]
216 | DataDir, get_database_name(MyDatabaseId));
| ^~~~~~~~~~~~~~~~~
| GetDatabasePath
zhparser.c:215:61: warning: format ‘%s’ expects argument of type ‘char *’, but argument 5 has type ‘int’ [-Wformat=]
215 | snprintf(dict_path, MAXPGPATH, "%s/base/zhprs_dict_%s.txt",
| ~^
| |
| char *
| %d
216 | DataDir, get_database_name(MyDatabaseId));
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
| |
| int

Then create extension and run example query:

-- create the extension
CREATE EXTENSION zhparser;

-- make test configuration using parser
CREATE TEXT SEARCH CONFIGURATION testzhcfg (PARSER = zhparser);

-- add token mapping
ALTER TEXT SEARCH CONFIGURATION testzhcfg ADD MAPPING FOR n,v,a,i,e,l WITH simple;

-- ts_parse
SELECT * FROM ts_parse('zhparser', 'hello world! 2010年保障房建设在全国范围内获全面启动，从中央到地方纷纷加大 了保障房的建设和投入力度 。2011年，保障房进入了更大规模的建设阶段。住房城乡建设部党组书记、部长姜伟新去年底在全国住房城乡建设工作会议上表示，要继续推进保障性安居工程建设。');

Crash happens:
server closed the connection unexpectedly
This probably means the server terminated abnormally
before or while processing the request.
The connection to the server was lost. Attempting reset: Succeeded.

[amutu]

Thanks for your patch!