to_float and parse_float should have the same implementation

[pront]

While working on #1107, I realized that parse_float doesn't share the same implementation as to_float. The latter has a more generic implementation that can replace the former. Same for to_int and parse_int.

Since 0.43 these deviated, see playground example (needs VRL version v.20.0).

[pront]

Ref: vectordotdev/vector#21970 (motivation for fixing this)

[pront]

to_int and parse_int are not straightforward because the latter supports multiple bases. We could refactor the code but IMO it is a low priority task.

[pront]

#1120 (comment)