fix: tx prioritization (backport #101)

[mergify]

• pass the entire pay amount (amount used in --fee) into the txPriority calculation. This incorporates a notion of "payment over the base fee" that is used to actually derive your priority. We retain dividing by gas limit so that priority is denominated in "gas price"
• the Coin passed into the priority calculation will always be resolved to the feemarket base fee. This calculation is always truncated when going from DecCoins to Coins
• Refactor GetTxPriority to scale the values to integers. Previously, when gasPrices were < 1, nearly all priorities would just be truncated to 0. Added fuzz testing around this

  ---

  This is an automatic backport of pull request fix: tx prioritization  #101 done by Mergify.

[mergify]

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Changes to be committed:
	modified:   x/feemarket/ante/fee.go
	new file:   x/feemarket/fuzz/tx_priority_test.go
	modified:   x/feemarket/post/fee_test.go

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	deleted by us:   tests/e2e/consumer.go

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