fix(codeLens): clear whole buffer on resolving

[fannheyward]

coc will resolve codeLens onChange/onMove etc, with codeLens in current visible range, then display in virtualText.

If the codeLens.position = top, and outside the current visible, coc won't clear them, and add another line in virtualText.

Clear all on resolving before setting again.

Closes https://github.com/fannheyward/coc-rust-analyzer/issues/1112