fix: Check for the getBaseTable API before calling it

[mofojed]

• If it's not available, just fallback to the getKeyTable API (which we were using before)
• Tested against deephaven-core 0.35.1

from deephaven import new_table

x = new_table({
    "Foo": [0, 1, 2, 0, 1, 2],
    "Bar": [4, 5, 6, 7, 8, 9]}
).partition_by(["Foo"])

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 7 lines in your changes missing coverage. Please review.

Project coverage is 46.67%. Comparing base (b741f4e) to head (115f3cf).

Files	Patch %	Lines
...ges/iris-grid/src/IrisGridPartitionedTableModel.ts	0.00%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2168      +/-   ##
==========================================
- Coverage   46.67%   46.67%   -0.01%     
==========================================
  Files         692      692              
  Lines       38622    38628       +6     
  Branches     9812     9839      +27     
==========================================
  Hits        18028    18028              
+ Misses      20583    20547      -36     
- Partials       11       53      +42     

Flag	Coverage Δ
unit	46.67% <0.00%> (-0.01%)	⬇️

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[AkshatJawne]

LGTM