[compiler] Improve error messages for unhandled terminal and instruction kinds (#32324)

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## Summary

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Explain the **motivation** for making this change. What existing problem
does the pull request solve?
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Improve the error message, as the value is currently an object instead
of a string, which results in it being converted to '[object Object]'.

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Already tested locally.
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Author: inottn

compiler/packages/babel-plugin-react-compiler/src/ReactiveScopes/PrintReactiveFunction.ts

@@ -394,7 +394,10 @@ function writeTerminal(writer: Writer, terminal: ReactiveTerminal): void {
       break;
     }
     default:
-      assertExhaustive(terminal, `Unhandled terminal ${terminal}`);
+      assertExhaustive(
+        terminal,
+        `Unhandled terminal kind \`${(terminal as any).kind}\``,
+      );
   }
 }
 

compiler/packages/babel-plugin-react-compiler/src/TypeInference/InferTypes.ts

@@ -420,7 +420,10 @@ function* generateInstructionTypes(
       break;
     }
     default:
-      assertExhaustive(value, `Unhandled instruction value kind: ${value}`);
+      assertExhaustive(
+        value,
+        `Unhandled instruction value kind: ${(value as any).kind}`,
+      );
   }
 }