fix: CometReader.loadVector should not overwrite dictionary ids

[viirya]

Which issue does this PR close?

Closes #475.

Rationale for this change

What changes are included in this PR?

How are these changes tested?

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 25 lines in your changes are missing coverage. Please review.

Project coverage is 34.03%. Comparing base (9125e6a) to head (0eb2ca6).
Report is 4 commits behind head on main.

Files	Patch %	Lines
...scala/org/apache/arrow/c/CometSchemaImporter.scala	0.00%	9 Missing ⚠️
...in/java/org/apache/comet/parquet/ColumnReader.java	0.00%	8 Missing ⚠️
.../scala/org/apache/spark/sql/comet/util/Utils.scala	0.00%	4 Missing ⚠️
...ain/java/org/apache/comet/parquet/BatchReader.java	0.00%	2 Missing ⚠️
...ava/org/apache/comet/parquet/LazyColumnReader.java	0.00%	1 Missing ⚠️
.../src/main/java/org/apache/comet/parquet/Utils.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #476      +/-   ##
============================================
- Coverage     34.05%   34.03%   -0.02%     
  Complexity      859      859              
============================================
  Files           116      117       +1     
  Lines         38680    38696      +16     
  Branches       8568     8567       -1     
============================================
  Hits          13171    13171              
- Misses        22746    22762      +16     
  Partials       2763     2763              

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[viirya]

cc @sunchao @andygrove

[viirya]

CometSchemaImporter now is implemented in Java.

[viirya]

@sunchao Any more comments? Thanks.

[viirya]

Merged. Thanks @andygrove @sunchao