[TASK] Use native str_starts_with() PHP method

One of our main utility methods "GeneralUtility::isFirstPartOfStr"
can now replaced by PHP's native "str_starts_with()" function
(see https://www.php.net/manual/en/function.str-starts-with.php)
which is also available for PHP 7.4 thanks to Symfony's polyfill
package.

This way, we can
a) slim down our own code base in favor of native PHP calls
b) add a bit of performance due to native PHP calls
c) move towards type-safety to ensure that we hand over strings
to these methods, as our own method was a bit more "lax" on things

Resolves: #95257
Releases: master
Change-Id: I70617ab4419849353a72a10dfed31a2d96f58072
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/70444


Tested-by: core-ci <typo3@b13.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>