[9.x] Add JSON grammar support to MySQL and SQLite schema usage

[LarsGrevelink]

Targets #36343 and laravel/ideas#2500. Now targets master due to the required change of the migrations as discussed in pull request #36363.

Adds JSON support for the Schema grammar when using them in virtual or stored columns. This makes the behaviour of referencing JSON columns the same as the Query grammar supports. Added support for both SQLite and MySQL since I was able to test these in real-life scenarios.

The current way of working with JSON data in columns requires to be e.g. MySQL specific;

Schema::table('my_table', function (Blueprint $table) {
    $table->string('my_extracted_value')->virtualAs('json_field->>"$.extract_me"');
});

This pull request applies the same grammar as the query grammar, already used within Laravel;

Schema::table('my_table', function (Blueprint $table) {
    $table->string('my_extracted_value')->virtualAs('json_field->extract_me');
});

If there are any questions related to the changes, please let me know.

[taylorotwell]

Renamed methods to virtualAsJson and storedAsJson so that people can still drop-down to raw behavior if needed.