> The tree-sitter-enabled function, `treesit-transpose-sexps',
> that is called by transpose-sexps, is broken.

After many unsuccessful attempts I finally arrived at the
usable implementation.  For example, typing 'C-M-t'
between two conditions:

if (x > 72 &&
    -!-y < 85) { // found
  do_something();
}

swaps these two conditions:

if (y < 85 &&
    x > 72) { // found
  do_something();
}

whereas inside the binary expression

if (x > -!-72 &&
    y < 85) { // found
  do_something();
}

it swaps its components:

if (72 > x &&
    y < 85) { // found
  do_something();
}

Or with point between two objects in an array:

var a = [{
  case: 'zzzz',
  default: 'yyyy'
},
-!-{
  case: 'zzzz2',
  default: 'yyyy'
}];

it swaps these objects:

var a = [{
  case: 'zzzz2',
  default: 'yyyy'
},
{
  case: 'zzzz',
  default: 'yyyy'
}];

whereas with point between two pairs

var a = [{
  case: 'zzzz',
  -!-default: 'yyyy'
}];

it swaps these pairs

var a = [{
  default: 'yyyy',
  case: 'zzzz'
}];

while keeping the right punctuation.

In a string it falls back to the default function.