[Blazor] Invoke inbound activity handlers on circuit initialization

[MackinnonBuck]

[Blazor] Invoke inbound activity handlers on circuit initialization

Fixes an issue where inbound activity handlers don't get invoked on circuit initialization.

Description

[!NOTE] This bug only affects Blazor Server apps, not Blazor Web apps utilizing server interactivity

Changes:

• Updated CircuitHost to invoke inbound activity handlers on circuit initialization
• Added an extra test to verify that inbound activity handlers work on the initial page load
• Updated existing Blazor Web tests to reuse test logic from the non-web tests
  • The previous web-specific tests were not as elaborate, so this helps to ensure that the feature works the same way on Blazor Server and Blazor Web

Fixes #57481