fixrule(aria_hidden_nontabbable) improve group mesage

[philljenkins]

Reword group message:

"group": "A focusable element should not be within the subtree of an element with 'aria-hidden' set to \"true\"",

to
"group": "A hidden element should not contain any tabbable elements",

as discussed during ruleID consistency review

existing ruleID.ts file containing message
https://github.com/IBMa/equal-access/blob/master/accessibility-checker-engine/src/v4/rules/aria_hidden_focus_misuse.ts

[philljenkins]

ruleID was changed to aria_hidden_nontabbable during ruleID consistency work:
"group": "A focusable element should not be within the subtree of an element with 'aria-hidden' set to \"true\"",
change to
"group": "A hidden element should not contain any tabbable elements",

• "group" message is displayed in Help, not in test files, so no changes are needed in test cases.
• "group" message changed in rule and baselines files

[philljenkins]

PR #1506 assigned to @shunguoy for review

[philljenkins]

This is a screenshot of the "old" group message displayed in the Help

[philljenkins]

The new build will show the group message replaced by the new message
The "group" message is the lighter title after the Violation in the banner
New group message is: "A hidden element should not contain any tabbable elements"

[ErickRenteria]

Validated