Change exceptions to extend Error.

This changes exception classes generated for `--target thrift-server` so that they extend `ErrorThriftLike` instead of `ThriftLike`. There's a corresponding `thrift-server` change to add the `ErrorThriftLike` class.

As mentioned in [the GitHub issue](creditkarma#178), this is useful because it causes Thrift exceptions to have stack traces and because some frameworks expect exceptions to derive from Error. The GitHub issue mentions graphql-js. Jest's `toThrow()` function would also benefit from this. Here's an example:

```
await expect(thriftClient.someFunction()).rejects.toThrow()
```

`toThrow` doesn't identify Thrift exceptions as exceptions because they don't derive from Error and so it will return false in such cases. Part of the blame could fall on Jest, because perhaps `toThrow` should return true for any rejected promise regardless of the type of object being throw, but I think some of the blame still falls on Thrift.

A downside of extending Error is that there's a naming collision when developers define fields named `name`, `message`, `stack`, etc in their Thrift exceptions (because these are defined by the super class). I think this is an acceptable tradeoff. FYI `tsc` complains if someone defines a field that differs from the super class. For example, if someone has a Thrift exception with `1: required i32 message` (because message must be a string) or `1: optional string message` (because message is required).

I tried to avoid the naming collisions by manually adding Error to the exception class's prototype chain. It might avoid the tsc compile errors when there's a naming collision but it doesn't really eliminate the problem of same-named fields being used for two different things. And so I think manually changing the prototype chain is a bad solution.

Remaining work:
- Fix tests.
- Update README.md to mention that end-users need to require the new version of thrift-server which includes `ErrorThrifTLike`.
- Update README.me to mention the naming collision limitation.
- `tsc` complains for naming collisions, and that's fine. Maybe the Thrift compiler should check for and report on collisions? Would probably be a friendly user experience. One challenge is [different JS implementations define different properties on their Error class](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error#Instance_properties).
- I didn't change the code generated for `--target apache`. It looks like those classes also don't derive from Error. They probably should.

src/main/render/thrift-server/exception/index.ts

@@ -10,5 +10,5 @@ export function renderException(
     node: ExceptionDefinition,
     state: IRenderState,
 ): Array<ts.Statement> {
-    return renderStruct(node, state)
+    return renderStruct(node, state, true)
 }

src/main/render/thrift-server/identifiers.ts

@@ -33,6 +33,7 @@ export const THRIFT_IDENTIFIERS = {
         'thrift.InputBufferUnderrunError',
     ),
     StructLike: ts.createIdentifier('thrift.StructLike'),
+    ErrorStructLike: ts.createIdentifier('thrift.ErrorStructLike'),
 }
 
 export const THRIFT_TYPES = {

src/main/render/thrift-server/struct/class.ts

@@ -27,6 +27,7 @@ import {
     classNameForStruct,
     createSuperCall,
     extendsAbstract,
+    extendsAbstractError,
     implementsInterface,
     looseNameForStruct,
     throwForField,
@@ -38,6 +39,7 @@ export function renderClass(
     node: InterfaceWithFields,
     state: IRenderState,
     isExported: boolean,
+    extendError: boolean = false,
 ): ts.ClassDeclaration {
     const fields: Array<ts.PropertyDeclaration> = [
         ...createFieldsForStruct(node, state),
@@ -97,7 +99,10 @@ export function renderClass(
         tokens(isExported),
         classNameForStruct(node, state).replace('__NAMESPACE__', ''),
         [],
-        [extendsAbstract(), implementsInterface(node, state)], // heritage
+        [
+            extendError ? extendsAbstractError() : extendsAbstract(),
+            implementsInterface(node, state),
+        ], // heritage
         [
             ...fields,
             ctor,

src/main/render/thrift-server/struct/index.ts

@@ -13,10 +13,11 @@ import { renderClass } from './class'
 export function renderStruct(
     node: InterfaceWithFields,
     state: IRenderState,
+    extendError: boolean = false,
 ): Array<ts.Statement> {
     return [
         ...renderInterface(node, state, true),
         renderToolkit(node, state, true),
-        renderClass(node, state, true),
+        renderClass(node, state, true, extendError),
     ]
 }

src/main/render/thrift-server/struct/utils.ts

@@ -133,6 +133,15 @@ export function extendsAbstract(): ts.HeritageClause {
     ])
 }
 
+export function extendsAbstractError(): ts.HeritageClause {
+    return ts.createHeritageClause(ts.SyntaxKind.ExtendsKeyword, [
+        ts.createExpressionWithTypeArguments(
+            [],
+            THRIFT_IDENTIFIERS.ErrorStructLike,
+        ),
+    ])
+}
+
 export function implementsInterface(
     node: InterfaceWithFields,
     state: IRenderState,