[5.0 -> main] Benchmark BLS host functions, Do not require trailing = for base64 encoded strings

[heifner]

Merging release/5.0 into main including #1889 & #1892 (all empty commits superseded by #1888) and #1884.

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Add benchmarking of BLS host functions into Leap Benchmark suites. Those host functions are directly benchmarked without using CDT wrappers.

Use benchmark/benchmark -f bls to benchmark. A sample result looks like

function                    runs        average       minimum       maximum

bls:
bls_g1_add                  1,000       2,736 ns       2,607 ns      10,048 ns
bls_g2_add                  1,000       6,766 ns       6,461 ns      13,983 ns
bls_g1_mul                  1,000     193,676 ns     191,533 ns     204,904 ns
bls_g2_mul                  1,000     486,744 ns     480,722 ns     516,755 ns
bls_pairing 1 pair          1,000   1,284,147 ns   1,263,355 ns   1,521,806 ns
bls_pairing 3 pairs         1,000   2,095,239 ns   2,060,983 ns   2,448,659 ns
bls_g1_exp 1 point          1,000     491,239 ns     485,616 ns     626,591 ns
bls_g1_exp 3 points         1,000     698,879 ns     692,786 ns     741,049 ns
bls_g2_exp 1 point          1,000   1,239,919 ns   1,229,475 ns   1,559,680 ns
bls_g2_exp 3 points         1,000   1,841,482 ns   1,821,692 ns   2,167,092 ns
bls_g1_map                  1,000     297,041 ns     291,710 ns     310,379 ns
bls_g2_map                  1,000     380,135 ns     374,088 ns     438,751 ns
bls_fp_mod                  1,000         764 ns         668 ns       7,571 ns

Resolves #1854

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These changes superseded by #1888.

All previous versions of nodeos required a trailing = for base64 encoded strings. fc::variant appends an extra = for all of its base64 encoded strings. However, non-fc base64 encoders do not add an extra = when one is not needed. This PR modifies fc::variant to support non-fc base64 encoded strings that do not have the extra =.

In 5.0, fc::variant was updated to not add the extra = to base64 encoded strings. See #1888. This PR allows nodeos to support the new 5.0 version of base64 encoded strings.

Empty diff because changes already part of #1888

Issue #1461

[linh2931]

Thanks @heifner for merging the benchmarking PR together for me.