build: fix rollup globals for examples package

[devversion]

Recently the rollup globals have been changed because the operators are no longer applied to the prototype (using /add/ imports).

This now causes some warnigns and invalid id's in the bundles of the Material examples because those still use the /add/ imports in some examples.

Note: In theory we can also generate this object automatically as well, but since those are less operator it should be fine.

@jelbourn In the future I think it would be better if we also have a rollup-config.js file for every package? (as in Angular core)

[jelbourn]

LGTM

I don't see any harm in having this one config for all the package since it doesn't have any effect if you don't use the symbol.

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