feat: only inject push/init/pop when necessary

[Rich-Harris]

closes #11297. TODO:

• remove $$props argument where possible
• identify 'safe' call expressions/member expressions

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[dummdidumm]

Found a false negative, see comment.
Also: Do we really need the "needs props" logic? Seems totally harmless to have an unused parameter, it's going to get treeshaken out - not sure it's worth the additional code/maintenance

[Rich-Harris]

Obviously it'll differ from tool to tool, but unused parameters are not treeshaken out by Rollup, because that would affect fn.length which is dangerous. But if you remove the parameter yourself, Rollup is able to throw out the corresponding arguments:

(We can't just omit the props when calling the function, because then the child component would need to be defensive, which would undo the gains and then some)