Added arrowkey navigation to modals

[blackbaud-conorwright]

Allowed and defaulted focus to the modal-content region for arrow key scrolling. Also added the role=region and aria-labelledby for proper aria labeling.

Resolves: #1479

[codecov-io]

Codecov Report

Merging #1809 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master   #1809    +/-   ##
=======================================
  Coverage     100%    100%            
=======================================
  Files         424     416     -8     
  Lines        8980    8765   -215     
  Branches     1328    1294    -34     
=======================================
- Hits         8980    8765   -215

Impacted Files	Coverage Δ
src/modules/modal/modal.component.ts	100% <100%> (ø)	⬆️
src/modules/radio/radio.component.ts	100% <0%> (ø)	⬆️
src/modules/text-expand/text-expand.component.ts	100% <0%> (ø)	⬆️
src/modules/checkbox/checkbox.component.ts	100% <0%> (ø)	⬆️
src/modules/flyout/flyout.component.ts	100% <0%> (ø)	⬆️
src/modules/wait/wait.module.ts	100% <0%> (ø)	⬆️
...modules/list-view-grid/list-view-grid.component.ts	100% <0%> (ø)	⬆️
src/modules/grid/grid.module.ts	100% <0%> (ø)	⬆️
src/modules/radio/radio.module.ts	100% <0%> (ø)	⬆️
...-expand-repeater/text-expand-repeater.component.ts	100% <0%> (ø)	⬆️
... and 14 more

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[Blackbaud-MattGregg]

@blackbaud-conorwright I honestly don't know how screen readers would react to this. This seems like something to set up and test via keyboard and then with screen readers (JAWS in particular as that is the one we seem to be getting customer complaints and questions about).

[Blackbaud-TrevorBurch]

LGTM