[LSP] Additional Text Edits support for class import

[dantleech]

It should be relatively simply to support additional text edits, to support with the neovim_LanguageClient

• The primary suggestion must be a TextEdit (with the correct start and end offsets). Wil need to support returning the start position in the completion library.
• The new suggestion's (line) position should be offset by any additional edits,
• We can probably build a bridge for the existing TextEditBuilder to support returning TextEdit instances.

This feature may incur a performance penalty (e.g. it has to calculate the import edits for each importable suggestion). So it should be configurable.