…Chart/ContourPlot/TernaryPlot (apache#4238)

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### What changes were proposed in this PR?
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This PR fixes a bug in `BubbleChartOpDesc`, `ContourPlotOpDesc`, and
`TernaryPlotOpDesc` where boolean fields were interpolated into the
Python template without quotes, resulting in code like `if false ==
'true'`. Since Python does not recognize lowercase false as a valid
identifier, this caused a `NameError: name 'false' is not defined`. The
fix wraps the variables in quotes (`if '$enableColor' == 'true'`),
reverting to the string comparison approach used before the Python
template was introduced, so the generated Python performs a
string-to-string comparison.

Demo:
<img width="700" height="738" alt="bubblechart"
src="https://github.com/user-attachments/assets/d2811da5-beb9-4d8d-89f8-cca544f93e68"
/>

### Any related issues, documentation, discussions?
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Closes apache#4257 

### How was this PR tested?
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Manually tested

### Was this PR authored or co-authored using generative AI tooling?
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No

---------

Co-authored-by: carloea2 <carloea2@uci.edu>
Co-authored-by: Xinyuan Lin <xinyual3@uci.edu>