More precise flow step navigation

[wwong]

Hacking some stuff together for my own use. I'll separate this out into two distinct PRs later - one for viewing by GHAS alert numbers and another for the step navigation changes.

User-facing changes:

• Ability to view alerts by GHAS alert number. UI with my changes is kind of clunky and could use a refactor before making a real PR
• Making navigation to flow steps more precise - text selection will take the line and column starts/ends into account rather than just the start line
• Bug fixes
  • Put steps into a scroll pane so that it doesn't take over the entire sidebar
  • Un-nested some of the jump-to-line code in step navigation (would previously get skipped because steps didn't have a ruleDescription to pass into openFile)
  • Copypasta in the row onClick handler for steps: https://github.com/advanced-security/SARIF-viewer/blob/main/src/main/kotlin/com/github/adrienpessu/sarifviewer/toolWindow/SarifViewerWindowFactory.kt#L541