[3.x] Update TinyMCE

[SniperSister]

Summary of Changes

This PR updates tinymce to version 4.5.12 - this is the highest version we can include in Joomla 3 due to browser support.

It also fixes numerous security issues.

Changelog:

Fixed so links with xlink:href attributes are filtered correctly to prevent XSS. #TINY-1626
Fixed the selection.setContent() API not running parser filters #TINY-4002
Fixed the visualchars plugin converting HTML-like text to DOM elements in certain cases #TINY-4507
Fixed HTML comments incorrectly being parsed in certain cases #TINY-4511
Fixed a security issue related to CDATA sanitization during parsing #TINY-4669
Fixed content in an iframe element parsing as dom elements instead of text content #TINY-5943

[SniperSister]

/cc @joomla/security

[brianteeman]

is the admin-item-edit js supposed to be here?

[SniperSister]

@brianteeman whoops, good catch, fixed

[zero-24]

I have tested this item ✅ successfully on d98c59e

Looks good to me, thanks @SniperSister

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[richard67]

I have tested this item ✅ successfully on d98c59e

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[richard67]

RTC

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[wilsonge]

Thanks guys!