fixrule(a_text_purpose, meta_viewport_zoomable, widget_tabbable_exists, widget_tabbable_single): Re-mapping WCAG SC and help references

[shunguoy]

Rule/Engine updates:
fixrule(a_text_purpose, meta_viewport_zoomable): Re-mapping WCAG SC

• New Rule(s): List rule IDs
• New or modified help files: meta_viewport_zoomable.html
• Rule bug: a_text_purpose, meta_viewport_zoomable

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

• fixes: fixrule(a_text_purpose) to report against (map) both 4.1.2 Name, Role, Value and 2.4.4 Link Purpose (In Context) to match ACT #1468
• fixes: fixrule(meta_viewport_zoomable) to report against (map) only 1.4.4 Resize text and not 1.4.10 Reflow to match ACT #1469
• fixes [BUG]: Reported in Slack - Potential mis-assignment of error to 2.4.3 Focus Order rather than 2.1.1 Keyboard #1834

Additional information can be found here:

Testing reference:

• test cases: test/v2/checker/accessibility/rules/meta_viewport_zoomable_ruleunit/viewport_fail_maximum_user_scale_1.0.html
  Click "Learn More" for Recommendation Message: Confirm the 'meta[name=viewport]' with "maximum-scale=1.0" can be zoomed by user
• Before fix: Two SC mappings (Requirements): IBM 1.4.4 Resize text and IBM 1.4.10 Reflow
• After fix: only one SC mapping (Requirements): IBM 1.4.4 Resize text
• Review the mapping in the Checker rule set for the rules mapped to 1.4.4, 1.4.10, 2.1.1 and 2..4.3. The mapping is also available in the Actions -> Artifacts: Rule listing (generated are build time)
• Review the help text changes for the widget_tabbable_single rule

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.

[shunguoy]

@philljenkins I reviewed your changes. Please go ahead to review the rest and push to test.

[philljenkins]

Reviewed code changes

[philljenkins]

Reviewed mapping changes are correct in Action artifact Rule listing

[philljenkins]

changes and mapping reviewed and ready for QA

[ErickRenteria]

@shunguoy we also need to remove the requirements under why is this important?

[shunguoy]

@ErickRenteria fixed, thanks.