Feature: #66445 - Add file extension to mimeType mapping

See Issue #66445

Description

As a fix for wrong mimeType detection for SVG files without XML prologue we added a new setting to map known file extensions to mimeTypes. The new setting is $GLOBALS['TYPO3_CONF_VARS']['SYS']['FileInfo']['fileExtensionToMimeType'] which contains an array:

array(
        'svg' => 'image/svg+xml'
)

Impact

The automatic detection for mimeTypes works great, but in some special cases not. This new setting should only be used, if the automatic detection fails.