send textDocument/didSave only if the server supports it

[prabirshrestha]

• Don't send notification if it is of type TextDocumentSyncKind.

capabilities {
    textDocumentSync: TextDocumentSyncKind.Full,
}

• Send notification only if it says it supports.

capabilities: {
    textDocumentSync: {
        save: {}
    }
}

• Send notification along with the text only if includeText is true.

capabilities: {
    textDocumentSync: {
        save: {
            includeText: true
        }
    }
}