[Feature] Expression.map

[jaychia]

Summary

Add an expression to map values from one domain to another.

Proposal

df = DataFrame.from_pydict({"foo": [1, 2, 3]})
df = df.with_column("foo_mapped", df["foo"].map({1: "one", 2: "two"}))

df.collect()

# +-----+
# | foo |
# +-----+
# | one |
# | two |
# | null|
# +-----+