Add advanced type definition for Atlas Search Indexes

[GromNaN]

Extracted from #3230

Main issues:

• Support of completion by PHPStorm of not good
  • https://youtrack.jetbrains.com/issue/WI-60979/Support-for-phpstan-type-in-autocomplete-alias-to-array-shape)
  • https://youtrack.jetbrains.com/issue/WI-75416/Support-multiline-psalm-array-declaration-with-comments
• Support of nested array shapes by PHPStan produces difficult to read error messages: https://phpstan.org/r/412cb41e-4002-44fa-86fc-386236eab654
• The server team will update the definition.

  We will be changing the schema of index definitions constantly. I'd say multiple times a year. For instance stemmerName takes one of ~20 string values and we will probably remove 3 of them soon. Mostly though we are extending the syntax.

[GromNaN]

Related issue for advanced array shapes: symfony/symfony#58771