Install adapters return extension ID on success

[mbabker]

Summary of Changes

JInstallerAdapter::install() and JInstallerAdapter::update() return the extension ID of the installed/updated extension on success, these methods do not only return boolean values. Fixed the docs.

Testing Instructions

Review

Documentation Changes Required

Already done 😉

[andrepereiradasilva]

I have tested this item ✅ successfully on ce9ce1e

on code review

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[jeckodevelopment]

I have tested this item ✅ successfully on ce9ce1e

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/13039.}