Revert "[babel] Remove unused PipelineError"

This reverts commit 10d129a8406e9d226abdb6943bf8512e34ce91db 

--- 

Reverts #2311 due to undocumented assumptions being broken. I also added some 
comments to `LoggerEvents` to explain each event type. 

In `Program.ts`, we have something like the following code. `compile` could 
produce any number of errors (not just expected errors / instances of 
`CompilerError`). As an example, we sometimes error in `Codegen` due to babel 
version incompatibilities (`Error: ObjectMethod: Too many arguments passed. 
Received 7 but can receive no more than 5`). 

```js 

try { 

// any error could be thrown here 

compile(input); 

} catch (e) { 

// unknown type for e 

handleError(e, ...); 

} 

```

compiler/packages/babel-plugin-react-forget/src/Entrypoint/Options.ts

@@ -138,6 +138,11 @@ export type LoggerEvent =
       fnLoc: t.SourceLocation | null;
       fnName: string | null;
       memoSlots: number;
+    }
+  | {
+      kind: "PipelineError";
+      fnLoc: t.SourceLocation | null;
+      data: any;
     };
 
 export type Logger = {

compiler/packages/babel-plugin-react-forget/src/Entrypoint/Program.ts

@@ -66,16 +66,31 @@ type CompileResult = {
 };
 
 function handleError(
-  err: CompilerError,
+  err: unknown,
   pass: CompilerPass,
   fnLoc: t.SourceLocation | null
 ): void {
   if (pass.opts.logger) {
-    for (const detail of err.details) {
+    if (err instanceof CompilerError) {
+      for (const detail of err.details) {
+        pass.opts.logger.logEvent(pass.filename, {
+          kind: "CompileError",
+          fnLoc,
+          detail: detail.options,
+        });
+      }
+    } else {
+      let stringifiedError;
+      if (err instanceof Error) {
+        stringifiedError = err.stack ?? err.message;
+      } else {
+        stringifiedError = err?.toString() ?? "[ null ]";
+      }
+
       pass.opts.logger.logEvent(pass.filename, {
-        kind: "CompileError",
+        kind: "PipelineError",
         fnLoc,
-        detail: detail.options,
+        data: stringifiedError,
       });
     }
   }