Migrate Bounded Types to Const Generics

[shawntabrizi]

I believe const generics were not stable when we first introduced bounded types.

Now that they are, we should use them instead of Get<u32> which may allow a runtime developer to shoot themselves in the foot by NOT providing a constant value.

This should not be a breaking change other than syntax.

[shawntabrizi]

Seems like we cannot complete this PR yet:

error: generic parameters may not be used in const operations
   --> frame/balances/src/lib.rs:529:45
    |
529 |         WeakBoundedVec<BalanceLock<T::Balance>, { T::MAX_LOCKS }>,
    |                                                   ^^^^^^^^^^^^ cannot perform const operation using `T`
    |
    = note: type parameters may not be used in const expressions

Need this feature to stabilize.

rust-lang/rust#60551 (comment)