perf: generate switch statement for oneof union encode

[antsluts]

Updates the encode method to generate a switch statement for oneof unions. These are currently generating as if statements for every possible $case so not great for performance as the number of cases grows.

In our usage scenario we have a oneof with 160+ cases, which is currently generating 160+ if statements and during encode each is evaluated!!!

From benchmarking against our internal .proto message definition the switch version achieves ~2.8x better performance over the current if version.

Before

export const Value = {
  encode(message: Value, writer: _m0.Writer = _m0.Writer.create()): _m0.Writer {
    if (message.kind?.$case === "null_value") {
      writer.uint32(8).int32(message.kind.null_value);
    }
    if (message.kind?.$case === "number_value") {   // not an 'else if' so evaluate regardless if matched already
      writer.uint32(17).double(message.kind.number_value);
    }
    if (message.kind?.$case === "string_value") {   // not an 'else if' so evaluate regardless if matched already
      writer.uint32(26).string(message.kind.string_value);
    }
    ...

After

export const Value = {
  encode(message: Value, writer: _m0.Writer = _m0.Writer.create()): _m0.Writer {
    switch (message.kind?.$case) {
      case "null_value":
        writer.uint32(8).int32(message.kind.null_value);
        break;
      case "number_value":
        writer.uint32(17).double(message.kind.number_value);
        break;
      case "string_value":
        writer.uint32(26).string(message.kind.string_value);
        break;
     ...

[stephenh]

Looks great, thanks @antsluts !

[stephenh]

🎉 This PR is included in version 1.139.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release
• v1.139.0

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