Improve instruction benchmarks (#9712)

* seal_input can be called multiple times

* Increase size of instruction benchmarks

* Remove randomness from instr_br* benchmarks

* cargo run --quiet --release --features=runtime-benchmarks --manifest-path=bin/node/cli/Cargo.toml -- benchmark --chain=dev --steps=50 --repeat=20 --pallet=pallet_contracts --extrinsic=* --execution=wasm --wasm-execution=compiled --heap-pages=4096 --output=./frame/contracts/src/weights.rs --template=./.maintain/frame-weight-template.hbs

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