Updates to LiquidityPositionsResponse

[grod220]

After attempting a UI for LP positions in penumbra-zone/web#1786, there are some changes to LiquidityPositionsResponse that would make it easier to create LP-related UI's.

Proposal

message LiquidityPositionsResponse {
      Position data = 1;
+    PositionId position_id = 2;
+    SpendableNoteRecord note_record = 3;
+    ValueView r1_value_view = 4;
+    ValueView r2_value_view = 5;
}

Reasons for the additions:

• position_id prevents the need for consumers to match the index in the request with the response
• note_record allows the response to contain the associated LP NFT. This allows subsequent requests to close/withdraw to know which source account to use for fees. Otherwise, the consumer needs to request all balances and do the matching themselves (an expensive operation). This would quite likely require database work to associate position ID's with base denoms.
• The two ValueView's are used to display metadata of the reserve assets to users can see icons and amounts in the display denom format. If not returned, the consumer needs to roundtrip two assetMetadataById() requests