#### Drop support for the old "import assertions" syntax (#18611 by @fisker)

`import assertions` (using the `assert` keyword) is an old version of the current [import attributes proposal](https://github.com/tc39/proposal-import-attributes).

```js
// Old (deprecated)
import foo from "./foo.json" assert { type: "json" };

// Current standard
import foo from "./foo.json" with { type: "json" };
```

Babel 8 completely removed support for the legacy `assert` syntax (the old parser plugin is gone).
Without Babel parser support, Prettier can no longer reliably parse or format code using `import ... assert { ... }`.

Please migrate to the `with` syntax.

```diff
- import foo from "./foo.json" assert { type: "json" };
+ import foo from "./foo.json" with   { type: "json" };
```

See also Prettier's [disclaimer about non-standard syntax](https://prettier.io/docs/rationale.html#disclaimer-about-non-standard-syntax).
