## What This PR Does
1. Recover on, and provide a better message for, invalid `export` modifier on constructor parameters. Before, an `unexpected token` error would be produced and the parser would panic. Now, the parser recovers and produces a message saying `'export' modifier cannot appear on a parameter.`
```ts
class Foo {
constructor(export x: number) {}
}
```
2. Recover on, and provide a better message for, invalid modifiers on index signatures. Same recovery/message characteristics as above.
```ts
class Foo {
public [x: string]: string;
}
```
## What This PR Does
Provide better error messages when a reserved word is used as a `BindingIdentifier`
```ts
var const = 1;
export enum const {}
const if = 1;
```
Our convention is that AST type fields are ordered in order they appear in source. Move `type_parameters` fields in TS function declaration types to before `this_param` and formal parameters.
Use `BindingIdentifier` instead of `IdentifierName` so that AST visitors can access the bound symbol id for the namespace's name. This makes namespace consistent with other named declarations, such as `Class`, `Function`, and `TSInterfaceDeclaration`.
We should consider modifying `TSModuleDeclarationName::StringLiteral(...)` to also store a `symbol_id`, since one gets bound in semantic for it as well.
Quality-of-life improvement for invalid `const` modifiers on class elements. Instead of panicking, the parser will eat `const` and report it as an error.
```ts
class C {
static const H = 1;
}
```
An alternative version of #6177.
Convert `ModuleImports` into a common transform. Works much as before, but it inserts `import` / `require` statements by passing them to `TopLevelStatements` common transform, so they get inserted in one go with any other inserted top-level statements. This avoids shuffling up the `Vec<Statement>` multiple times, which can be slow with large files.
`VarDeclarations` also inserts any declarations via `TopLevelStatements` but runs after `ModuleImports`, so can control whether a `var` statement is inserted before or after `import` statements by inserting it via `VarDeclarations` (to appear after `import` statements) or directly into `TopLevelStatements` (to appear before `import` statements). Insertion order is not actually important, but allows us to match Babel's output and pass its tests.
