Remove or split up Frame methods that use the index

[vyasr]

This PR contributes to excising indexes from Frame and moving them entirely to IndexedFrame. A number of methods (such as copy, equals, and _mimic_inplace) have either been removed from Frame or had the index-related logic moved to corresponding function overrides in IndexedFrame. In the process, this PR also implements certain optimizations as part of the rewrite. Of particular interest is that because indexes are immutable, IndexedFrame.copy has been modified to always shallow copy the index, which should significantly reduce memory pressure in copy-heavy applications. This also results in significant performance improvements when the Index is not a RangeIndex, for example:

In [2]: df = cudf.DataFrame({"a": range(10000), "b": range(10000)}, index=[i*2 for i in range(10000)])
# Before
In [3]: %timeit df.copy(deep=True)
151 µs ± 2.05 µs per loop (mean ± std. dev. of 7 runs, 10,000 loops each)
# After
In [3]: %timeit df.copy(deep=True)
119 µs ± 804 ns per loop (mean ± std. dev. of 7 runs, 10,000 loops each)

Other methods rewritten in this PR have also been sped up, although the speedups are typically more modest. For example:

# Using the same DataFrame as above
# Before
In [4]: %timeit df.clip(100, 1000)
489 µs ± 4.39 µs per loop (mean ± std. dev. of 7 runs, 1,000 loops each)
# After
In [4]: %timeit df.clip(100, 1000)
431 µs ± 2.42 µs per loop (mean ± std. dev. of 7 runs, 1,000 loops each)

[codecov]

Codecov Report

Merging #10439 (ddbc468) into branch-22.04 (21ed251) will increase coverage by 0.19%.
The diff coverage is 100.00%.

❗ Current head ddbc468 differs from pull request most recent head 4f109fe. Consider uploading reports for the commit 4f109fe to get more accurate results

@@               Coverage Diff                @@
##           branch-22.04   #10439      +/-   ##
================================================
+ Coverage         85.95%   86.15%   +0.19%     
================================================
  Files               139      139              
  Lines             22435    22447      +12     
================================================
+ Hits              19285    19340      +55     
+ Misses             3150     3107      -43     

Impacted Files	Coverage Δ
python/cudf/cudf/core/column_accessor.py	93.47% <100.00%> (+0.04%)	⬆️
python/cudf/cudf/core/dataframe.py	93.58% <100.00%> (+<0.01%)	⬆️
python/cudf/cudf/core/frame.py	91.84% <100.00%> (+<0.01%)	⬆️
python/cudf/cudf/core/index.py	92.27% <100.00%> (+0.04%)	⬆️
python/cudf/cudf/core/indexed_frame.py	92.97% <100.00%> (+0.67%)	⬆️
python/cudf/cudf/core/multiindex.py	92.14% <100.00%> (-0.02%)	⬇️
python/cudf/cudf/core/series.py	95.16% <100.00%> (ø)
python/cudf/cudf/core/single_column_frame.py	96.85% <100.00%> (-0.17%)	⬇️
python/cudf/cudf/core/column/string.py	88.91% <0.00%> (+0.12%)	⬆️
... and 4 more

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[vyasr]

rerun tests

[isVoid]

Just a small comment below.

[vyasr]

@gpucibot merge