Fix Blazor WebAssembly diagnostics defaults to use the defined opt-out property

[Copilot]

Blazor WebAssembly diagnostics defaults were wired to two different property names. The SDK set BlazorWebAssemblyDiagnosticsEnabled, but the default conditions for MetricsSupport, EventSourceSupport, and HttpActivityPropagationSupport checked BlazorWasmDiagnosticsEnabled, so those switches never defaulted on.

• SDK property wiring

  • Update Microsoft.NET.Sdk.BlazorWebAssembly.Current.props so all three diagnostics feature switches key off BlazorWebAssemblyDiagnosticsEnabled
  • Align the comment/documented opt-out property with the actual property name

• Regression coverage

  • Add a focused Blazor WebAssembly test that verifies:
    • default evaluation enables all three switches
    • setting BlazorWebAssemblyDiagnosticsEnabled=false disables all three

<BlazorWebAssemblyDiagnosticsEnabled Condition="'$(BlazorWebAssemblyDiagnosticsEnabled)' == ''">true</BlazorWebAssemblyDiagnosticsEnabled>
<MetricsSupport Condition="'$(MetricsSupport)' == '' and '$(BlazorWebAssemblyDiagnosticsEnabled)' == 'true'">true</MetricsSupport>
<EventSourceSupport Condition="'$(EventSourceSupport)' == '' and '$(BlazorWebAssemblyDiagnosticsEnabled)' == 'true'">true</EventSourceSupport>
<HttpActivityPropagationSupport Condition="'$(HttpActivityPropagationSupport)' == '' and '$(BlazorWebAssemblyDiagnosticsEnabled)' == 'true'">true</HttpActivityPropagationSupport>

• Fixes Blazor WASM diagnostics feature switches never default on (BlazorWasmDiagnosticsEnabled vs BlazorWebAssemblyDiagnosticsEnabled property mismatch) #55446

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