Add IE11 support forced color mode tweaks

Adds IE11 support to the previous Windows High Contrast Mode fixes in PR

Internet Explorer 11 doesn't support the `forced-colors` media feature
or the `forced-color-adjust` property, but it has equivalents in
`-ms-high-contrast` and `-ms-high-contrast-adjust`.
We can use those CSS features to extend fixes to high contrast mode that
previously only worked on more modern browsers.

Adds a tweak to changes in commit 7dcba7d, so that the highlight works
in Internet Explorer 11 as well.

CHANGELOG.md

@@ -10,6 +10,7 @@ We’ve made fixes to GOV.UK Frontend in the following pull requests:
 - [#2265: Don’t remove focus outline from disabled link buttons in forced color mode](https://github.com/alphagov/govuk-frontend/pull/2265)
 - [#2273: Fix invisible footer OGL logo in forced color mode](https://github.com/alphagov/govuk-frontend/pull/2273) – thanks to [@oscarduignan](https://github.com/oscarduignan) for reporting this issue.
 - [#2277: Fix invisible start button chevron in forced color mode](https://github.com/alphagov/govuk-frontend/pull/2277)
+- [#2290: Improve support for IE11 with Windows High Contrast Mode](https://github.com/alphagov/govuk-frontend/pull/2290)
 
 ## 3.13.0 (Feature release)
 

src/govuk/components/checkboxes/_index.scss

@@ -132,7 +132,7 @@
 
     // When in an explicit forced-color mode, we can use the Highlight system
     // color for the outline to better match focus states of native controls
-    @media screen and (forced-colors: active) {
+    @media screen and (forced-colors: active), (-ms-high-contrast: active) {
       outline-color: Highlight;
     }
 

src/govuk/components/radios/_index.scss

@@ -130,7 +130,7 @@
 
     // When in an explicit forced-color mode, we can use the Highlight system
     // color for the outline to better match focus states of native controls
-    @media screen and (forced-colors: active) {
+    @media screen and (forced-colors: active), (-ms-high-contrast: active) {
       outline-color: Highlight;
     }