Add MSBuild Server lifecycle node support (binlog format v27)

[JanProvaznik]

Companion to dotnet/msbuild#14156, which records how each build relates to the MSBuild Server node as a dedicated MSBuildServerLifecycleEventArgs, serialized under its own BinaryLogRecordKind.MSBuildServerLifecycle (binary-log format version 27).

This teaches the viewer to read and render that record.

Changes

• Read the new MSBuildServerLifecycle record (BuildEventArgsReader + a vendored MSBuildServerLifecycleEventArgs).
• Render it as a dedicated MSBuildServerNode under a "MSBuild Server" folder, with a distinct icon (WPF Generic.xaml + Avalonia). The node exposes Kind (Spawned / Reused / NotUsed), ShortLived, ProcessId, Reason and ReasonCode.
• Also read the LoggersRegistered record (format v26). Without this, opening a v26/v27 binlog reports "Skipped some data unknown to this version of Viewer" for that record; it is now surfaced as an ordinary message.

Behavior for the four server scenarios

Scenario	Node
cold build	Kind=Spawned
next build	Kind=Reused (same PID)
-nr:false (non-/mt)	Kind=NotUsed, ReasonCode=node-reuse-disabled
/mt -nr:false	Kind=Spawned, ShortLived=True

Notes

• The record kind is backward-compatible: older viewers that predate it skip it gracefully (it is length-prefixed and its minimum-reader-version is unchanged). This PR simply lets the viewer render it instead of skipping.
• MSBuildServerNode serializes as a Message (like TimedMessage/MessageWithLocation) so .buildlog round-tripping is unaffected; the dedicated CLR type still drives the distinct icon.
• Draft pending the MSBuild side (Log MSBuild Server lifecycle (spawn/reuse/not-used) to the build log dotnet/msbuild#14156) merging and the format version being finalized.

[KirillOsenkov]

if we confirm that we're absolutely sure we want to rev the binlog format, then this looks fine. If @baronfel says go ahead you can undraft and I can merge and publish the viewer first, then we can test binlogs produced by the MSBuild PR to make sure it works, then merge the MSBuild PR then.

[JanProvaznik]

tested with local build of viewer