Fix browserName typo for Edge WebView2 - #8455

Description

MsEdgeDriver lets clients request the browserName = "webview2" capability to drive native apps using the WebView2 control. Selenium users can set this using the EdgeOptions.UseWebView property.

Turns out there are a couple problems with this property's implementation:

1. It was attempting to use "WebView2" as the browserName, but msedgedriver expects "webview2" (lowercase)
2. An abstract property was added to the ChromiumDriver base class so that Edge and Chrome could supply whatever browserName values they wanted, but this property was being read only once on construction. Setting EdgeOptions.UseWebView = true wouldn't actually change the browserName.

Motivation and Context

Fixing a regression due to the introduction of the .UseWebView property.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• I have read the contributing document.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.