Open GitHub PR and issue links to the side when VS Code requests it - #9151

VS Code passes viewColumn: ViewColumn.Beside to external URI openers when a link is opened with an open-to-side gesture (e.g. Alt+Enter in Quick Open). The GitHub issue/PR opener ignored it, so the overview always opened or revealed in the current editor group.

Changes

• externalUriOpener.ts: the opener now maps openContext.viewColumn === vscode.ViewColumn.Beside to toTheSide and passes it to PullRequestOverviewPanel.createOrShow and IssueOverviewPanel.createOrShow. Placement was already implemented in both panels via _getViewColumn:
  • New panel → createWebviewPanel(..., ViewColumn.Beside, ...)
  • Existing panel → reveal(ViewColumn.Beside, true), which moves it to the side group without taking focus, as for any other reveal.
  • No column or Active → behaviour is unchanged. Only Beside is honoured; other columns open in the current group.
• Tests (externalUriOpener.test.ts), each run for both PRs and issues:
  • A side request creates a new panel beside the active editor.
  • A side request reveals an already-open panel beside.
  • With no column or Active, a new panel still opens in the active group and an existing panel is revealed with undefined (stays where it is).

const toTheSide = openContext.viewColumn === vscode.ViewColumn.Beside;
await PullRequestOverviewPanel.createOrShow(telemetry, extensionUri, manager, identity, pullRequest, toTheSide);

• Fixes Honor open-to-side placement when opening GitHub PR and issue links #9072