High contrast CSS properties scanner (#2580)
#### Details
Implemented Edge deprecated high contrast CSS properties scanner.
Request
```
[
{
"url": "https://accessibilityinsights.io/",
"priority": 100,
"deepScan": false,
"browserValidations": ["highContrastProperties"],
"site": {
"baseUrl": "https://accessibilityinsights.io/",
"knownPages": []
}
}
]
```
Response
```
{
"scanId": "11111111-0000-0000-0000-37b05484db3e",
"url": "https://accessibilityinsights.io/",
"scanType": "accessibility",
"scanResult": {
"state": "pass"
},
"browserValidationResult": {
"highContrastProperties": "pending | pass | fail"
},
...
}
```
#### Pull request checklist
<!-- If a checklist item is not applicable to this change, write "n/a"
in the checkbox -->
- [ ] Addresses an existing issue: Fixes #0000
- [x] Added relevant unit test for your changes. (`yarn test`)
- [ ] Verified code coverage for the changes made. Check coverage report
at: `<rootDir>/test-results/unit/coverage`
- [ ] Ran precheckin (`yarn precheckin`)
- [x] Validated in an Azure resource group
a6e27fbab7