• Added DashToolKind and DashTool.kind to distinguish top-level tools from
  shared components, plus DashTool.canBeRootTool.
• Added shared-component DashTool values: analysisServer
  (analysis-server), dartMcpServer (dart-mcp-server), and skillsCli
  (skills-cli).
• topLevelTool() now ignores a DASH__TOOL value that names a shared
  component and falls back to the current tool.
• Deprecated topLevelTool(). Tools no longer need to read DASH__TOOL
  themselves: pass your own tool to Analytics, which resolves the root tool,
  and use getEnvironment() for child processes.
• Analytics now resolves the root tool (the user's entry point) from
  DASH__TOOL, then an optional new fallbackRootTool parameter on
  Analytics and Analytics.development, then the tool itself. Only tools,
  never shared components, can be the root tool.
• Every event now carries two new user properties: root_tool, the resolved
  root tool, and leaf_tool, the logical tool passed as tool to Analytics
  (a top-level tool or a shared component).
• The tool user property keeps its current value, the tool itself for a
  top-level tool and the root tool for a shared component, so existing
  dashboards keep working. It's deprecated and will be removed in a future
  release.
• LogFileStats.toolCount now counts events by leaf tool, falling back to
  tool for log records written before leaf_tool existed.
• Added fallbackRootTool and rootTool (a test-only override) parameters to
  Analytics.fake, which resolves DASH__TOOL from its environment.
• Opt-in status, the first-run and consent-message-version checks,
  clientShowedMessage(), and getConsentMessage are now keyed on the root
  tool instead of the tool. A shared component never shows its own consent
  message or gets its own line in the config file.
• If no root tool resolves, which can only happen for a shared component,
  analytics are disabled for the session, in internal builds too: the
  Analytics factories return a NoOpAnalytics, and other instances report
  okToSend == false, show no consent message, and never write to the config
  file.
• Fixed getEnvironment() to set DASH__TOOL to the tool's label (for
  example vscode-plugins) instead of its Dart enum name (vscodePlugins),
  which DashTool.fromLabel rejected. It now passes on the resolved root
  tool, so a shared component never passes on itself, and leaves out
  DASH__TOOL when no root tool resolves.