fix: number of prepend lines sent to LSP

[heyzec]

The extension tells the LSP server how many lines of code at prepended, which the LSP server uses to determine where to insert imports. The current implementation is bugged and does not consider the marker lines, causing the LSP to add auto imports inside the prepend section instead of below.

[heyzec]

We can consider removing the nPrependLines argument being passed to the LSP. Instead, the LSP uses the end marker to determine where to add its imports.

[mug1wara26]

lgtm, my only concern with the lsp auto detecting the end of prepend is if there are no prepended lines, the current change does not place any markers right? If there was no prepend marker, the user could insert their own and lead to unexpected behaviour. This isn't too big of an issue cause its very unlikely someone would put // END PREPEND in their own code, but it is still not intended behaviour.