@mcap/support: remove .d.ts file in favor of module augmentation in s…

…ource file (#1318)

### Changelog
@mcap/support: Fixed a TS error from an import that did not work in the
published package

### Docs

None

### Description

Supersedes / closes #1300 
See also protobufjs/protobuf.js#1499

This area of TypeScript arcana is confusing, but I don't think there is
anything about [module
augmentations](https://www.typescriptlang.org/docs/handbook/declaration-merging.html#module-augmentation)
that requires them to be in a `.d.ts` file.

The way it's currently done was generally working, except as pointed out
in #1300 we didn't include the `typings` dir in the published package.

I believe we didn't run into this problem in our own code because we
usually turn on `"skipLibCheck": true`.

typescript/support/src/protobufDescriptors.ts

@@ -1,8 +1,16 @@
-// eslint-disable-next-line @typescript-eslint/triple-slash-reference
-/// <reference path="../typings/protobufjs.d.ts" />
-
 import protobufjs from "protobufjs";
-import { FileDescriptorSet } from "protobufjs/ext/descriptor";
+import { FileDescriptorSet, IFileDescriptorSet } from "protobufjs/ext/descriptor";
+
+// https://github.com/protobufjs/protobuf.js/issues/1499
+declare module "protobufjs" {
+  interface ReflectionObject {
+    toDescriptor(protoVersion: string): protobufjs.Message<IFileDescriptorSet> & IFileDescriptorSet;
+  }
+  // eslint-disable-next-line @typescript-eslint/no-namespace
+  namespace ReflectionObject {
+    const fromDescriptor: (desc: protobufjs.Message) => protobufjs.Root;
+  }
+}
 
 export type ProtobufDescriptor = ReturnType<protobufjs.Root["toDescriptor"]>;