Remove Bower, Grunt, and Gulp from primary docs

[JoshuaKGoldberg]

Following #846: the site's homepage and other docs around builders and package managers were last redone back when the web ecosystem was very different. In particular, the following were still in common popular use:

• Build systems: Grunt and Gulp
• Package managers: Bower was still

Those are no longer the case. Most users don't want to know about them anymore.

Proposal: let's remove them from the primary docs, and instead mention their equivalents:

• Build systems: I don't know what to replace them with... Just, nothing? npm scripts?
• Package managers: npm, pnpm, and yarn

I think it would make sense to leave "older" docs around in some capacity. Some older projects still use those things. Gulp in particular I think is still supported and has some users who appreciate its streaming capacities.

[eddiemonge]

As yeoman is meant to be opinionated, adding modern day replacements would be welcome. Perhaps recommend vite as it seems to be the most popular currently.

Package managers are mostly similar in the exposed API and so anytime a command from one is recommended, the code block that shows the commands could have tabs for how to install using each of them.

[mshima]

I suppose the referred part is https://github.com/yeoman/yeoman.io/blob/main/app/index.html#L55-L76.

No build system is supported by yo. They are generator specific, we probably should mention build systems when mentioning generator-webapp only.

npm/yarn/pnp package managers are supported by generator/environments apis.
this.packageJson and related apis on generator side. package.json file modification check, auto install and package manager detection on the environment side.

My suggestion is to drop build system or move to a dedicated section mentioning generator-webapp.