Handle MultimapKeysSideInput in State GetRequests

[damondouglas]

This PR closes #31628 adding handling for MultimapKeysSideInput in State GetRequests. Since this surfaced in Java validation tests of org.apache.beam.sdk.transforms.ViewTest, validated on Prism via:

TEST=org.apache.beam.sdk.transforms.ViewTest
./gradlew :runners:portability:java:ulrLoopbackValidatesRunnerTests -PjobEndpoint=localhost:8073 --tests="$TEST"

This PR fixes the following ViewTest tests:

• testMapAsEntrySetSideInput
• testWindowedMultimapAsEntrySetSideInput
• testWindowedMapAsEntrySetSideInput
• testMultimapAsEntrySetSideInput

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[damondouglas]

R: @lostluck

[github-actions]

Stopping reviewer notifications for this pull request: review requested by someone other than the bot, ceding control

[lostluck]

Approved after import fix.