Fix broken paste in iOS 13

[msamsel]

What is the purpose of this pull request?

Bug fix

Does your PR contain necessary tests?

All patches which change the editor code must include tests. You can always read more
on PR testing,
how to set the testing environment and
how to create tests
in the official CKEditor documentation.

This PR contains

• Unit tests
• Manual tests

What is the proposed changelog entry for this pull request?

*[#3354](/~https://github.com/ckeditor/ckeditor4/issues/3354) Fix: Broken paste in iOS 13.

What changes did you make?

Mark current iOS Safari version as supported for custom copy/cut and mark it as trusted browsers. This flags generally change the way how we treat pasted and copied data:

ckeditor4/plugins/clipboard/plugin.js

Lines 2249 to 2271 in 98cae96

	if ( !this.isCustomCopyCutSupported ) {
	// Edge < 16 does not support custom copy/cut, but it has some useful data in the clipboardData (https://dev.ckeditor.com/ticket/13755).
	return new this.dataTransfer( ( CKEDITOR.env.edge && evt && evt.data.$ && evt.data.$.clipboardData ) || null, sourceEditor );
	} else if ( evt && evt.data && evt.data.$ ) {
	var clipboardData = evt.data.$.clipboardData,
	dataTransfer = new this.dataTransfer( clipboardData, sourceEditor );
	// Set dataTransfer.id only for 'copy'/'cut' events (so for events initializing dataTransfer inside editor) (#962).
	if ( evt.name === 'copy' || evt.name === 'cut' ) {
	dataTransfer.storeId();
	}
	if ( this.copyCutData && dataTransfer.id == this.copyCutData.id ) {
	dataTransfer = this.copyCutData;
	dataTransfer.$ = clipboardData;
	} else {
	this.copyCutData = dataTransfer;
	}
	return dataTransfer;
	} else {
	return new this.dataTransfer( null, sourceEditor );
	}

It looks like a bug which is reported here: https://bugs.webkit.org/show_bug.cgi?id=19893#c34 no longer occur in iOS Safari.
The current version of Safari supports custom data types applied in data transfer.

As tests were already there covering those features I just simple activate them. I also re-activate manual tests.

Closes #3354

[f1ames]

Rebased onto latest major.

[f1ames]

LGTM 👍 Good job 🎉