CP-17536 - fixing the options for checkbox/radio; removing dead code

[niden]

Hello!

• Type: bug fix
• Link to issue: [BUG]: Forms\Element\CheckGroup and RadioGroup options are stored incorrectly #17536

In raising this pull request, I confirm the following:

• I have read and understood the Contributing Guidelines
• I have checked that another pull request for this purpose does not exist
• I wrote some tests for this PR
• I have updated the relevant CHANGELOG
• I have created a PR for the documentation about this change

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• Phalcon\Forms\Element\CheckGroup and RadioGroup storing their choices in the property Phalcon\Forms\Element\AbstractElement uses for user options, so setUserOption() added a choice and setOptions() removed every user option.
• Phalcon\Forms\Element\Select::addOption() writing with an offset into an object or null options value; the write now happens only when the options value is an array (null becomes an empty array).

Thanks