chore(tachometer): fix remote branches

[nolanlawson]

Details

At some point our Tachometer scripts got messed up, and when it tries to compare against a remote branch (e.g. master) it fails because NX thinks that the @lwc/perf-benchmarks-components project doesn't exist.

$ yarn build:performance:components
NX   Cannot find project '@lwc/perf-benchmarks-components'

This seems to be something subtle with how we were copying directory around (maybe NX is using symlinks under the hood or something)? Doing yarn install after copying these files, and copying only the necessary source files, seems to fix the issue.

Does this pull request introduce a breaking change?

• 😮‍💨 No, it does not introduce a breaking change.

Does this pull request introduce an observable change?

• 🤞 No, it does not introduce an observable change.

[nolanlawson]

One downside of this is that we are no longer copying package.json either... but I think this is actually preferable given its contents:

lwc/packages/@lwc/perf-benchmarks-components/package.json

Lines 8 to 10 in a7c6e78

	"devDependencies": {
	"@lwc/rollup-plugin": "7.2.3"
	},

We actually don't want to pin to a particular version of @lwc/rollup-plugin – the versions may differ between the current branch and master, so you want to use the version from master instead. I think the only reason this worked before was because yarn install was called before we copied the directories, so we never re-fetched any packages from npm, so it actually just used the local @lwc/rollup-plugin.

If we ever add dependencies here or something then that could cause issues... but we can cross that bridge when/if we get there.