SQLite

     Internal helper to apply an SEE key to a just-opened
     database. Requires that db be-a DB object which has just been
     opened, opt be the options object processed by its ctor, and opt
     must have either the key, hexkey, or textkey properties, either
     as a string, an ArrayBuffer, or a Uint8Array.

     This is a no-op in non-SEE builds. It throws on error and returns
     without side effects if none of the key/textkey/hexkey options
     are set. It throws if more than one is set or if any are set to
     values of an invalid type.

     Returns true if it applies the key, else an unspecified falsy value.
  */
  const dbCtorApplySEEKey = function(db,opt){
    if( !capi.sqlite3_key_v2 ) return;
    let keytype;
    let key;
    const check = (opt.key ? 1 : 0) + (opt.hexkey ? 1 : 0) + (opt.textkey ? 1 : 0);
    if( !check ) return;
    else if( check>1 ){
      toss3(capi.SQLITE_MISUSE,
            "Only ONE of (key, hexkey, textkey) may be provided.");
    }
    if( opt.key ){
      /* It is not legal to bind an argument to PRAGMA key=?, so we
         convert it to a hexkey... */
      keytype = 'key';
      key = opt.key;
      if('string'===typeof key){
        key = new TextEncoder('utf-8').encode(key);
      }
      if((key instanceof ArrayBuffer) || (key instanceof Uint8Array)){
        key = byteArrayToHex(key);
        keytype = 'hexkey';
      }else{
        toss3(capi.SQLITE_MISUSE,
              "Invalid value for the 'key' option. Expecting a string,",
              "ArrayBuffer, or Uint8Array.");
        return;
      }
    }else if( opt.textkey ){
      /* For textkey we need it to be in string form, so convert it to
         a string if it's a byte array... */
      keytype = 'textkey';
      key = opt.textkey;
      if(key instanceof ArrayBuffer){
        key = new Uint8Array(key);
      }
      if(key instanceof Uint8Array){
        key = new TextDecoder('utf-8').decode(key);
      }else if('string'!==typeof key){
        toss3(capi.SQLITE_MISUSE,
              "Invalid value for the 'textkey' option. Expecting a string,",
              "ArrayBuffer, or Uint8Array.");
      }
    }else if( opt.hexkey ){
      keytype = 'hexkey';
      key = opt.hexkey;
      if((key instanceof ArrayBuffer) || (key instanceof Uint8Array)){
        key = byteArrayToHex(key);
      }else if('string'!==typeof key){
        toss3(capi.SQLITE_MISUSE,
              "Invalid value for the 'hexkey' option. Expecting a string,",
              "ArrayBuffer, or Uint8Array.");
      }
      /* else assume it's valid hex codes */
    }else{
      return;
    }
    let stmt;
    try{

     properties:

     - `filename`: database file name
     - `flags`: open-mode flags
     - `vfs`: the VFS fname

//#if enable-see

     SEE-capable builds optionally support ONE of the following
     additional options:

     - `key`, `hexkey`, or `textkey`: encryption key as a string,
       ArrayBuffer, or Uint8Array. These flags function as documented
       for the SEE pragmas of the same names. Using a byte array for
       `hexkey` is equivalent to the same series of hex codes in
       string form, so `'666f6f'` is equivalent to
       `Uint8Array([0x66,0x6f,0x6f])`. A `textkey` byte array is
       assumed to be UTF-8. A `key` string is transformed into a UTF-8
       byte array, and a `key` byte array is transformed into a
       `hexkey` with the same bytes.

     In non-SEE builds, these options are ignored. In SEE builds,
     `PRAGMA key/textkey/hexkey=X` is executed immediately after
     opening the db. If more than one of the options is provided,
     or any option has an invalid argument type, an exception is
     thrown.

     Note that some DB subclasses may run post-initialization SQL
     code, e.g. to set a busy-handler timeout or tweak the page cache
     size. Such code is run _after_ the SEE key is applied. If no key
     is supplied and the database is encrypted, execution of the
     post-initialization SQL will fail, causing the constructor to
     throw.

//#endif enable-see

     The `filename` and `vfs` arguments may be either JS strings or
     C-strings allocated via WASM. `flags` is required to be a JS
     string (because it's specific to this API, which is specific
     to JS).

       If called with exactly 2 arguments and the 2nd is an object,
       that object is treated as the 2nd argument to the parent
       constructor.

       The exception's message is created by concatenating its
       arguments with a space between each, except for the
       two-args-with-an-object form and that the first argument will
       get coerced to a string, as described above, if it's an
       integer.

       If passed an integer first argument, the error object's
       `resultCode` member will be set to the given integer value,
       else it will be set to capi.SQLITE_ERROR.
    */