SyntaxError: 'super' keyword unexpected here

Hi @evanw ,
I was trying to upgrade a codebase which is using `esbuild` to produce compiled output.
After upgrading the `c12` package which also upgraded `exsolve`, esbuild produces wrong code for the `node10` target.

Here is an excerpt of `exsolve` to reproduce the issue on [esbuild try](https://esbuild.github.io/try/#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)

index.mjs

```javascript
function makeNodeErrorWithCode(Base, key) {
class NodeError extends Base {
code = key;
constructor(...args) {
assert.ok(args.length === 0, `Code: ${key}; The provided arguments length (${args.length}) does not match the required ones (${expectedLength}).`);
super(message);
}
get ["constructor"]() {
return Base;
}
get [kIsNodeError]() {
return true;
}
toString() {
return `${this.name} [${key}]: ${this.message}`;
}
}
return NodeError;
}
makeNodeErrorWithCode(Error, 0);
```

When you run `esbuild` with
```shell
npx esbuild --bundle --minify=false --platform=node index.mjs --outfile=dist/index.js --target=node10
```
it is transpiled to the following

dist/index.js

```javascript
var __defProp = Object.defineProperty;
var __defNormalProp = (obj, key, value) => key in obj ? __defProp(obj, key, { enumerable: true, configurable: true, writable: true, value }) : obj[key] = value;
var __publicField = (obj, key, value) => __defNormalProp(obj, typeof key !== "symbol" ? key + "" : key, value);

// index.mjs
function makeNodeErrorWithCode(Base, key) {
class NodeError extends Base {
get ["constructor"]() {
var __super = (...args) => {
super(...args);
__publicField(this, "code", key);
return this;
};
return Base;
}
constructor(...args2) {
assert.ok(args2.length === 0, `Code: ${key}; The provided arguments length (${args2.length}) does not match the required ones (${expectedLength}).`);
__super(message);
}
get [kIsNodeError]() {
return true;
}
toString() {
return `${this.name} [${key}]: ${this.message}`;
}
}
return NodeError;
}
makeNodeErrorWithCode(Error, 0);
```

Now when you try to run this with `node ./dist/index.js`, you get the following error:
```shell
super(...args);
^^^^^

SyntaxError: 'super' keyword unexpected here
```

It looks like this block
```javascript
var __super = (...args) => {
super(...args);
__publicField(this, "code", key);
return this;
};
```
is placed in the wrong location.
It should be placed into the `constructor` instead.

Reproduce the issue with the linked esbuild try case or with index.mjs and the node10 command, then inspect the generated dist/index.js. Trace the lowering of the class field and computed constructor getter, focusing on where the __super helper is emitted. Done means the generated node10 output keeps super inside a valid class constructor context and runs without the reported SyntaxError.

Written by the indexing model from the issue text.