ENH: Reimplement and undeprecate DataFrame.lookup
#### Is your feature request related to a problem?

I seriously get the impression that Pandas is actively being sabotaged. As a case in point, `DataFrame.lookup` was deprecated in v1.2. The problems with this are:

1. The [doc for `DataFrame.lookup`](https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.DataFrame.lookup.html) says to see itself for an example. Well, there is no example in the doc page. The only example I'm aware of is [here](https://pandas.pydata.org/pandas-docs/stable/user_guide/indexing.html#looking-up-values-by-index-column-labels) instead which is a different page.
2. The [changelog](https://pandas.pydata.org/docs/whatsnew/v1.2.0.html#deprecations) for this deprecation points to [GH18682](https://github.com/pandas-dev/pandas/pull/18682) which looks to be wholly irrelevant to this change. A lot has gone wrong here.
3. There is significant user code that already uses `lookup`. Why break it? If the current implementation of `lookup` is suboptimal, shouldn't it be optimized instead?
4. It is extremely complicated to use `melt` when `lookup` works quite simply. For example, compare [this simple answer using `lookup`](https://stackoverflow.com/a/45487394/) with [this complicated answer using `melt`](https://stackoverflow.com/a/65722008/).

Does nobody review changes, docs, and release notes anymore prior to the release? It looks this way.

#### Describe the solution you'd like

1. Optimize `lookup` if attainable using `melt` or otherwise.
1. Undeprecate `lookup`.