overview ruler annotations don't get cleared when search term is cleared

[meganrogge]

Originally reported microsoft/vscode#147659 and can be repro'd in the demo

Steps to reproduce

1. search for a single letter with highlight all matches enabled
2. remove the search term
3. 🐛 the decorations are cleared, but their corresponding overview ruler decorations remain

[meganrogge]

The decorations get disposed of properly, but don't clear until a refresh of overview ruler happens -- for example, the buffer changes

[meganrogge]

In order to avoid refreshing every time a decoration is deleted, I'd rather do this once when clearDecorations happens. Currently, there isn't a way for the addon to communicate with overviewRuler though