[CodingStyle] Deprecate WrapEncapsedVariableInCurlyBracesRector

[TomasVotruba]

Deprecates WrapEncapsedVariableInCurlyBracesRector and removes it from the coding style level.

The rule only wraps a plain interpolated variable in curly braces:

 function run($world)
 {
-    echo "Hello $world!";
+    echo "Hello {$world}!";
 }

This is a pure coding standard preference with no real value:

• no PHP version deprecates "$var" — the syntax stays valid
• the actual deprecation, ${var} (PHP 8.2), is already covered by VariableInStringInterpolationFixerRector in the php82 set
• a coding standard tool is the right place for this

Follows the same shape as #8268 and #8269.