[10.x] Add charset and collation method to Blueprint

[gcazin]

Based on this PR (#49250) and this comment (#49250 (comment)), I have added the methods for collation and charset in the Blueprint class

Before:

Schema::table('foo', function (Blueprint $table) {
    $table->charset = 'utf8mb4';
    $table->collation = 'utf8mb4_unicode_ci';

    // ...
});

After:

Schema::table('foo', function (Blueprint $table) {
    $table->charset('utf8mb4');
    $table->collation('utf8mb4_unicode_ci');

    // ...
});