Fix a TypeScript code generation edge case (#3199)

This release fixes a regression in version 0.18.4 where using a TypeScript namespace that exports a class declaration combined with --keep-names and a --target of es2021 or earlier could cause esbuild to export the class from the namespace using an incorrect name (notice the assignment to X2._Y vs. X2.Y):

// Original code

// Old output (with --keep-names --target=es2021)
var X;
((X2) => {
  const _Y = class _Y {
  };
  __name(_Y, "Y");
  let Y = _Y;
  X2._Y = _Y;
})(X || (X = {}));

// New output (with --keep-names --target=es2021)
var X;
((X2) => {
  const _Y = class _Y {
  };
  __name(_Y, "Y");
  let Y = _Y;
  X2.Y = _Y;
})(X || (X = {}));

Fix a panic due to empty static class blocks (#3161)

This release fixes a bug where an internal invariant that was introduced in the previous release was sometimes violated, which then caused a panic. It happened when bundling code containing an empty static class block with both minification and bundling enabled.