[Bugfix] Re-enable Gemma3 for V1

[DarkLight1337]

• Fix mismatch between prompt replacement and image embeddings while merging multimodal embeddings when pad and scan is enabled in V1
• Fix consecutive newline and boi tokens breaking prompt replacement when pad and scan is enabled because \n\n\n\n is a single token that cannot be matched against \n\n
• Figure out the cause of [Bug]: Gemma3 Offline Batch Inference: Attempted to assign XXX multimodal tokens to YYY placeholders #14897
• Remove SupportsV0Only and update docs

FIX #14897
FIX #14963

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[DarkLight1337]

Merging this first since the Gemma3 issue seems to be solved.

[ywang96]

Thanks for the fix!

[WoosukKwon]

@DarkLight1337 Thanks for doing this! ❤️