[vscode] extend timeline proposed API updated in vscode 1.106.1 and align timeline view

[ndoschek]

Feature Description:

This proposed API is used by the @theia/timeline implementation.

See https://github.com/microsoft/vscode/blob/1.106.1/src/vscode-dts/vscode.proposed.timeline.d.ts

• detail was renamed to tooltip
• a few minor doc updates
• a few readonly modifier updates

Theia timeline view:

• we should use the hoverService to display the tooltip properly
• the iconPath was not used yet, should be a small change enhance the timeline view