Omit unset ranges for TextDocumentContentChangeEvent

The Typescript language server [checks ranges only for equality to `undefined`](https://github.com/microsoft/vscode-languageserver-node/blob/1ce790dd341a38da1fbf902cddc16ce456149de0/protocol/src/common/protocol.ts#L1915) to determine if a change is incremental.

This means that unset ranges need to be omitted completely from the generated messages instead of encoding them as `null`.

Fixes 9fans/acme-lsp#75

lsp/protocol/generate/tables.go

@@ -46,7 +46,7 @@ var goplsStar = map[prop]int{
 	{"Lit_SemanticTokensClientCapabilities_requests_full_Item1", "delta"}: nothing, // A.B.C.D
 	{"Lit_SemanticTokensOptions_full_Item1", "delta"}:                     nothing, // A.B.C.
 
-	{"Lit_TextDocumentContentChangeEvent_Item0", "range"}: wantStar, // == nil test
+	{"Lit_TextDocumentContentChangeEvent_Item0", "range"}: wantOptStar, // == nil test, TS LSP checks for undefined instead of null.
 
 	{"TextDocumentClientCapabilities", "codeAction"}:          wantOpt, // A.B.C.D
 	{"TextDocumentClientCapabilities", "completion"}:          wantOpt, // A.B.C.D