lldb-dap currently crashes when the first character is non ascii. This
is because we assume that the request column is ascii based instead of
UTF16 code units,
and end up in the middle of a character code point. causing an assertion
since we cannot not send invalid UTF-8 values.
This also handles the case in multilines and the column is outside the
range of the text.
Move completion description to the `CompletionItem.detail` property.
3ca7a72990