Revert "refactor(core): remove version placeholder workaround"

[mmalerba]

Reverts #16231

[devversion]

To provide more context about this: It had to be reverted because there is a transform when the code gets synced into Google3. e.g. new code is inserted that depends on the Version symbol to be imported.

This is actually causing exceptions as #16231 removed the imported Version symbol. We need a general discussion on how we want to manage versions.. This is not a high priority for now.

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