[php-src] Issue #23094: ext/intl: NumberFormatter::parse() and parseCurrency() use UTF-16 offsets for UTF-8 strings

Issue: https://github.com/php/php-src/issues/23094
Author: LamentXU123

### Description

This happens in my own app:
```php
  <?php

  $formatter = new NumberFormatter('en_US', NumberFormatter::DECIMAL);

  $prefix = "\u{1F600}"; // 😀 
  $input = $prefix . '123';
  $offset = strlen($prefix);

  var_dump(strlen($input));
  var_dump($offset);
  var_dump($formatter->parse(
      $input,
      NumberFormatter::TYPE_INT32,
      $offset
  ));
  var_dump($offset);
```
```
  int(7)
  int(4)
  int(3)
  int(5)
```
While I expect
```
  int(7)
  int(4)
  int(123)
  int(7)
```
The emoji occupies 4 bytes in the PHP UTF-8 string but 2 UTF-16 code units in ICU. Very sure this is the reason.

The input offset should be converted from a UTF-8 byte offset to a UTF-16 code-unit offset before calling ICU. Ehhhhhhh unfortunately I think this happens commonly throughout the code base. So I might be planning some bigger refactor to solve this. Buggy stuff.

Since this is a rather easy case to solve, I will open this as an issue here. If anyone want to start a contribution to the intl extension. They can try to solve this as a good head start. This should be easier than JIT bugs anyways. Feel free to open a PR :)

### PHP Version

```plain
All supported version.
```

### Operating System

N/A