Update @web/dev-server-esbuild dependencie esbuild to v0.21

[mantou132]

esbuild v0.21 support javascript decorators, this is useful for testing some decorator-based frameworks

evanw/esbuild#104 (comment)

[Westbrook]

Would you be interested in making a contribution with this update?

[favna]

From a quick test done by setting esbuild to ~0.21.5 in my package resolutions and nothing breaking outright I think it's as easy as just bumping the dependency and no breaking changes are incurred for web-dev-server but I can't say for sure.

• v0.20 of esbuild only affects Deno users
• v0.21 is the introduction of decorators and is considered breaking by Evan because when the developer desires the old style decorators implemented by TypeScript they have to add experimentalDecorators in their tsconfig (just like they would have to when using TS >5.0)