Declare alasql.compile(), FuncValue nodes and string -> operands in types

[assapir]

Closes #2585.

Type-only, types/alasql.d.ts:

• AlaSQL.compile(sql, databaseid?), returning AlaSQLCompiledStatement (AlaSQLStatement plus the .promise() helper alasql.compile attaches).
• FuncValue (funcid, args?) added to the ExpressionNode union.
• Op.right widened to ExpressionNode | string: a->b puts the bare name on the right as a string.

Verification

A strict consumer compiled against the new d.ts: 0 errors. The same consumer against develop:

TS2305: Module '"alasql"' has no exported member 'FuncValue'.
TS2339: Property 'compile' does not exist on type 'AlaSQL'.
TS2322: Type '"b"' is not assignable to type 'ExpressionNode | undefined'.

test2317.js passes.