fix: disable experimental decorator flag (#1828)

The `experimentalDecorators` flag is legacy from TypeScript 3.9.

Since then, decorators have gone through a large change and their new
syntax, which is enabled by default in TypeScript 5+, looks very
different.

Keeping this old flag enabled locks users into old decorator typings
which are deprecated, plus because of the way our defaults are applied
these flags are not overridable.

Instead, don't set `experimentalDecorators` at all, and have users opt
in to legacy syntax if they must.

This is technically breaking, but I'm pretty sure this will affect such
a negligible fraction of users that I think it's worth it.

---

By submitting this pull request, I confirm that my contribution is made
under the terms of the [Apache 2.0 license].

[Apache 2.0 license]: https://www.apache.org/licenses/LICENSE-2.0

Author: rix0rrr

src/tsconfig/compiler-options.ts

@@ -4,7 +4,6 @@ import * as Case from '../case';
 export const BASE_COMPILER_OPTIONS: ts.CompilerOptions = {
   alwaysStrict: true,
   declaration: true,
-  experimentalDecorators: true,
   incremental: true,
   lib: ['lib.es2020.d.ts'],
   module: ts.ModuleKind.CommonJS,

test/compiler.test.ts

@@ -484,7 +484,6 @@ function expectedTypeScriptConfig() {
       alwaysStrict: true,
       composite: false,
       declaration: true,
-      experimentalDecorators: true,
       incremental: true,
       inlineSourceMap: true,
       inlineSources: true,