BUGFIX: MediaBrowser's upload action shows empty flash message if file is too big

[mhsdesign]

expected (like in the standalone media browser)

actual (media browser insider neos ui):

interestingly the error works in the neos ui when one uses the media browsers drag and drop

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The existence of this bug was uncovered via #5528 because previously no validation error was shown and on upload the server just died:

Could not convert target type "Neos\Media\Domain\Model\Asset": Missing constructor argument "resource" for object of type "Neos\Media\Domain\Model\Asset".

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This bug was uncovered because translate() simply returns undefined, if not initialised. No error no fallback, nuthing.
Also while I18n.init() IS called, it doesnt actually initialise anything. For that

neos-development-collection/Neos.Neos/Resources/Public/JavaScript/index.js

Lines 23 to 27 in 847e464

	cachedFetch(Configuration.get("XliffUri")).then((xliffData) => {
	if (xliffData) {
	Localization.initTranslations(xliffData);
	}
	});

has to be invoked and that is done by adding the link.

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Notice also that ist not particularly keen of us to initialise I18n once in the host (neos.ui) and then in the iframe too. This is just extra work for the browser, and we dump the iframe after selecting the image.
Now my pr doenst improve that but there are ideas outlined here neos/neos-ui#3119 and the first step for a global translate api was already introduced via neos/neos-ui#3804.
Nothing for a bugfix to build up on though.

Checklist

• Code follows the PSR-2 coding style
• Tests have been created, run and adjusted as needed
• The PR is created against the lowest maintained branch
• Reviewer - PR Title is brief but complete and starts with FEATURE|TASK|BUGFIX
• Reviewer - The first section explains the change briefly for change-logs
• Reviewer - Breaking Changes are marked with !!! and have upgrade-instructions

[nezaniel]

Lgtm