pallet-mmr: RPC API and Runtime API work with block numbers (#12345)

* pallet-mmr: RPC API works with block_numbers

* fixes

* update rpc

* fmt

* final touches in the rpc

* temporary fix

* fix

* fmt

* docs

* Update lib.rs

* use NumberFor

* validate input

* update runtime

* convert block_number to u64

* small edit

* update runtime api

* test fix

* runtime fix

* update test function

* fmt

* fix nits

* remove block_num_to_leaf_index from runtime api

* Update frame/merkle-mountain-range/src/lib.rs

Co-authored-by: Robert Hambrock <roberthambrock@gmail.com>

* fix tests

* get the code to compile after merge

* get the tests to compile

* fix in tests?

* fix test

* Update frame/merkle-mountain-range/src/tests.rs

Co-authored-by: Adrian Catangiu <adrian@parity.io>

* Update frame/merkle-mountain-range/src/lib.rs

Co-authored-by: Adrian Catangiu <adrian@parity.io>

* Update primitives/merkle-mountain-range/src/lib.rs

Co-authored-by: Adrian Catangiu <adrian@parity.io>

* fix errors & nits

* change block_num_to_leaf_index

* don't make any assumptions

* Update frame/merkle-mountain-range/src/tests.rs

Co-authored-by: Adrian Catangiu <adrian@parity.io>

* Update frame/merkle-mountain-range/src/tests.rs

Co-authored-by: Adrian Catangiu <adrian@parity.io>

* Update frame/merkle-mountain-range/src/tests.rs

Co-authored-by: Adrian Catangiu <adrian@parity.io>

* fix

* small fix

* use best_known_block_number

* best_known_block_number instead of leaves_count

* more readable?

* remove warning

* Update frame/merkle-mountain-range/src/lib.rs

Co-authored-by: Robert Hambrock <roberthambrock@gmail.com>

* simplify

* update docs

* nits

* fmt & fix

* merge fixes

* fix

* small fix

* docs & nit fixes

* Nit fixes

* remove leaf_indices_to_block_numbers()

* fmt

Co-authored-by: Robert Hambrock <roberthambrock@gmail.com>
Co-authored-by: Adrian Catangiu <adrian@parity.io>