Log Message:
databases/sqlite3: Spruce up build options.

1. Document reasoning for each of the build-time options available and
   set a rubric for which ones to enable in future updates.

2. Enable some options that look well-justified.  I went through all
   the options at https://www.sqlite.org/compile.html, applied the
   rubric, and compared to several other general-purpose packaging
   systems.

(Happy to discuss and amend the rubric and the choice of options --
this should be viewed as a starting point for review, testing, and
tweaking, not an inviolably final decision.)

3. Nix PKG_OPTIONS that are default-on upstream -- these haven't done
   anything in a while.  If you want to add these back, then:

   (a) they should be in PKG_SUGGESTED_OPTIONS (because they're
       already enabled by default upstream), and

   (b) you'll have to set and test the appropriate SQLITE_OMIT_*
       option.

   Options removed:
   - deserialize (default-on upstream anyway)
   - fts (default-on upstream anyway)
   - sqlite3-dbstat (unconditionally enabled in pkgsrc now because
     needed by downstream packages)

   Options remaining:
   - icu

4. Nix some deprecated options like SQLITE_ENABLE_LOAD_EXTENSION.

Additions to CONFIGURE_ARGS:
--enable-fts3 (paranoia, default-on upstream anyway)
--enable-fts4 (paranoia, default-on upstream anyway)
--enable-fts5 (paranoia, default-on upstream anyway)
--enable-math (paranoia, default-on upstream anyway)
--enable-rtree (paranoia, default-on upstream anyway)
--enable-session

Removals from CONFIGURE_ARGS: none

Additions to CFLAGS:
-DSQLITE_ENABLE_DBSTAT_VTAB
-DSQLITE_ENABLE_FTS3_PARENTHESIS
-DSQLITE_ENABLE_HIDDEN_COLUMNS
-DSQLITE_ENABLE_STMTVTAB

Removals from CFLAGS:
-DSQLITE_ENABLE_LOAD_EXTENISON (default-on upstream now; need
  SQLITE_OMIT_LOAD_EXTENSION to reverse)
-DSQLITE_ENABLE_MATH_FUNCTIONS (replaced by --enable-math for better
  build-time error checking)

PR pkg/58448: databases/sqlite3 is missing dbstat option