Implemented MultiIndex.equal_levels

[itholic]

This PR proposes MultiIndex.equal_levels.

>>> kmidx1 = ks.MultiIndex.from_tuples([("a", "x"), ("b", "y"), ("c", "z")])
>>> kmidx2 = ks.MultiIndex.from_tuples([("b", "y"), ("a", "x"), ("c", "z")])
>>> kmidx1.equal_levels(kmidx2)
True

[codecov-io]

Codecov Report

Merging #1789 (d679dc2) into master (138c7b8) will decrease coverage by 0.03%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1789      +/-   ##
==========================================
- Coverage   94.64%   94.61%   -0.04%     
==========================================
  Files          49       49              
  Lines       10818    10724      -94     
==========================================
- Hits        10239    10146      -93     
+ Misses        579      578       -1     

Impacted Files	Coverage Δ
databricks/koalas/missing/indexes.py	100.00% <ø> (ø)
databricks/koalas/indexes.py	96.98% <100.00%> (+0.02%)	:arrow_up:
databricks/koalas/__init__.py	85.93% <0.00%> (-4.69%)	:arrow_down:
databricks/koalas/testing/utils.py	79.12% <0.00%> (-1.40%)	:arrow_down:
...ricks/koalas/tests/plot/test_series_plot_plotly.py	95.83% <0.00%> (-0.47%)	:arrow_down:
databricks/koalas/generic.py	92.79% <0.00%> (-0.13%)	:arrow_down:
databricks/koalas/plot/matplotlib.py	93.23% <0.00%> (-0.12%)	:arrow_down:
databricks/koalas/mlflow.py	95.12% <0.00%> (-0.12%)	:arrow_down:
databricks/koalas/indexing.py	92.53% <0.00%> (-0.10%)	:arrow_down:
databricks/koalas/plot/core.py	92.68% <0.00%> (-0.09%)	:arrow_down:
... and 16 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update 138c7b8...d679dc2. Read the comment docs.

[itholic]

Could someone double check this just once more? Seems fine to me.

[ueshin]

I'll take a look later. @itholic Could you push an empty or a merge commit to rerun tests as it's been a while since the last build.

[itholic]

Sure, thanks :)

[xinrong-meng]

https://issues.apache.org/jira/browse/SPARK-36435