setDimensions
Implement to handle when the number of rows and columns that fit into the terminal panel changes, for example when font size changes or when the panel is resized. The initial state of a terminal's dimensions should be treated as undefined
until this is triggered as the size of a terminal isn't known until it shows up in the user interface.
When dimensions are overridden by onDidOverrideDimensions, setDimensions
will continue to be called with the regular panel dimensions, allowing the extension continue to react dimension changes.
Parameters
dimensions
The new dimensions.