…ct HTTP method in CurlHttpClient (KurtThiemann)

This PR was submitted for the 7.2 branch but it was squashed and merged into the 6.4 branch instead.

Discussion
----------

[HttpClient] Always set CURLOPT_CUSTOMREQUEST to the correct HTTP method in CurlHttpClient

| Q             | A
| ------------- | ---
| Branch?       | 7.2
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| Issues        | Fix #59043
| License       | MIT

Currently, when sending a `HEAD` request and using a closure as the request body using `CurlHttpClient`, a `PUT` request instead of a HEAD request will be sent. This is because `CURLOPT_NOBODY` is set to make a `HEAD` request, but is overwritten by `CURLOPT_UPLOAD`, which is necessary to make curl call `CURLOPT_READFUNCTION`, but also sets the HTTP method to `PUT`.
The solution I am suggesting is to just always set `CURLOPT_CUSTOMREQUEST`, so the correct HTTP method will be used, no matter what other options are added.

This is mainly an issue in the PSR-18 wrapper, since PSR requests always have a request body stream, even if the body is empty. Since #58856, `Psr18Client` always passes a closure as the request body to the underlying HTTP client instead of just reading the entire request body stream into a string, as that made it impossible to upload large files.

While it would be possible to add an exception to `Psr18Client` to only add the request body if the method used commonly has a body, I think the better solution is to ensure that  `CurlHttpClient` always actually sends the type of request that it is asked to send.

Commits
-------

bfdf5d9 [HttpClient] Always set CURLOPT_CUSTOMREQUEST to the correct HTTP method in CurlHttpClient