fixrule(element_accesskey_labelled) fix the label requirement for the elements with accesskey attribute

[shunguoy]

• New or modified help files: element_accesskey_labelled
• Rule bug: element_accesskey_labelled

This PR is related to the following issue(s):

#916
#1772

Additional information can be found here:

Testing reference:

test case: test/v2/checker/accessibility/rules/element_accesskey_labelled_ruleunit/form_control_accesskey.html
After the fix, the Recommendation messages: "The HTML element with an assigned 'accesskey' attribute does not have an associated label" should be gone.

I have conducted the following for this PR:

• I validated this code in Chrome and FF
• I validated this fix in my local env
• I provided details for testing
• This PR has been reviewed and is ready for test
• I understand that the title of this PR will be used for the next release notes.

[philljenkins]

@shunguoy how do we fix the wdio automated testing bug for this branch/PR?

I just re-ran the job, with logging turned on, and now it has passed. So it is some king of a timing error.

[ErickRenteria]

Validated