Add support for lineFoldingOnly folding ranges

[dibarbet]

Fixes dotnet/vscode-csharp#7974
Unblocks #80944 (comment)

VSCode sets the lineFoldingOnly LSP capability, indicating it cannot handle multiple folding ranges that start on the same line as another range starts or ends on. Folding ranges that are not compatible are simply dropped.

While we cannot always do anything more than drop one of the ranges, we can choose which range to drop and we can sometimes adjust ranges so that they will not be dropped:

1. If two ranges start on the same line, we want to pick the inner range for folding.
2. If a range ends on the same line as another starts, we can attempt to shrink it by one line to handle common cases like an else block starting on the same line as the if block ended:

if (blah) {
    ...
} else {
    ...
}

This is done as a post processing step of the ranges. This seemed reasonable as the service generally independently constructs folding ranges based on the syntax and has little knowledge of what the other ranges will be produced (to know if they overlap)