test(runtime-core) Test polymorphic host functions with more types

[Hywan]

Partially extracted from #1018.

I was testing the new polymorphic host function API and noticed that Value::F32 and Value::F64 returns random values.

When running cd lib/runtime-core-tests; cargo test -- test_closure_dynamic_3, you will see random values for k (which is a f32):

One run:

[lib/runtime-core-tests/tests/imports.rs:239] i = 1
[lib/runtime-core-tests/tests/imports.rs:240] j = 2
[lib/runtime-core-tests/tests/imports.rs:241] k = 0.00000000000000000000000000000000000050528894

Another run:

[lib/runtime-core-tests/tests/imports.rs:239] i = 1
[lib/runtime-core-tests/tests/imports.rs:240] j = 2
[lib/runtime-core-tests/tests/imports.rs:241] k = 0.000000000000000000000000000000037134995

[Hywan]

This is where the outputs of the PR's description come from.

[losfair]

#1271 will fix this.