sqlite: replace the ANTLR parser with meyer

[kyleconroy]

meyer is a hand-written recursive descent parser for SQLite's dialect, ported from src/parse.y and src/tokenize.c and checked against SQLite itself. Moving to it deletes 1.2 MB of generated ANTLR code and the antlr4-go direct dependency, and replaces a grammar that only approximated SQLite with one that accepts what SQLite accepts.

This is step 8 of meyer's PLAN.md.

What changed

• parse.go calls meyer and slices statement extents out of the node spans. A parse failure becomes a sqlerr.Error positioned from meyer's byte offset, so syntax errors now report a line and column instead of a bare message.
• convert.go rewritten to map meyer's tree onto sql/ast.
• reserved.go defers to meyer's keyword table, which the hand-maintained list was missing MATERIALIZED and RETURNING from.
• internal/engine/sqlite/parser/ deleted. antlr4-go/antlr/v4 stays in go.mod as an indirect dependency of cel-go.

sqlc.arg() and friends

SQLite has no schema-qualified function call, so sqlc.arg(), sqlc.narg(), sqlc.slice() and sqlc.embed() are not SQL meyer will parse — the ANTLR grammar accepted them because it had a qualified_function_name rule SQLite does not.

The parser folds sqlc.name( to sqlc_name( before parsing and the converter puts the schema back. The fold walks meyer's token stream rather than the raw text, so it cannot reach inside a string literal or a comment; it substitutes one byte for another, so every offset in the tree still points at the same place in the original source, which is what rewrite/parameters.go and rewrite/embeds.go edit against; and it records the offsets it touched, so a user-defined sqlc_arg function is not mistaken for one.

Behavior the old grammar got wrong

• col TEXT NULL was read as a column whose type was TEXTNULL, because ANTLR's type_name swallowed the constraint. The column generated as interface{} rather than a nullable string. One golden file changes.
• GROUP BY was dropped whenever the query also had a WHERE clause, from an off-by-one over the ANTLR expression list. It only worked on queries with no WHERE.
• Comparison operators other than = were all recorded as = (there was a // TODO: add actual comparison), and IS, ISNULL, NOTNULL and LIKE reached the AST as = as well.
• ORDER BY, DISTINCT, WITH RECURSIVE, ON CONFLICT, OVER and FILTER were parsed and then discarded, so ast.Format dropped them from the SQL it rebuilds — which the expander relies on.
• Quoted identifiers other than "..." kept their quotes, and ""-escaped quotes inside one produced the empty string. Float literals became the integer 0.

Two changes outside the engine follow from these:

• internal/compiler/output_columns.go recognizes SQLite's implicit rowid / _rowid_ / oid. GROUP BY reaching the compiler for the first time means its column references are validated, and GROUP BY transactions.rowid in testdata/table_function would otherwise fail.
• lang.IsComparisonOperator learned the keyword-spelled comparisons (IS, IS NOT, LIKE, ISNULL, ...) so SELECT x IS NULL still types as bool now that the operator carries its own name. These are written upper case, which is how SQLite's parser records them; PostgreSQL and MySQL use distinct node types or their own operator spellings, so the strings do not overlap.

One capability is lost

The pinned SQLite build meyer targets defines neither SQLITE_ENABLE_UPDATE_DELETE_LIMIT nor SQLITE_UDL_CAPABLE_PARSER, so UPDATE and DELETE no longer accept ORDER BY or LIMIT. No test covered it, but anyone running against a build with that option compiled in would regress. Restoring it means a change in meyer, not here.

Also worth flagging: TRUE and FALSE are now column references rather than integer constants, because that is what SQLite's grammar does with them — they are resolved at name-resolution time, not tokenized as literals. Nothing in the test suite exercises it.

Testing

gofmt, go vet ./... and go test --tags=examples ./... all clean, against native PostgreSQL and MySQL: endtoend (TestReplay, TestFormat, TestExamples, TestExamplesVet, TestJsonSchema), the expander, and the sqlite examples. The endtoend suite is the acceptance gate; the sqlite engine's unit tests were removed.

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