Add solidity filter

[HaleySchuhl]

Describe your changes
A new function that filters objects based on their solidity.

Type of update
Is this a:

• New feature
• Work in progress

Associated issues
Merge after #1482

Additional context
Useful in filtering masks of pollen grains.

For the reviewer
See this page for instructions on how to review the pull request.

• PR functionality reviewed in a Jupyter Notebook
• All tests pass
• Test coverage remains 100%
• Documentation tested
• New documentation pages added to plantcv/mkdocs.yml
• Changes to function input/output signatures added to updating.md
• Code reviewed
• PR approved

[deepsource-io]

Here's the code health analysis summary for commits 127c358..ef7a9ab. View details on DeepSource ↗.

Analysis Summary

Analyzer	Status	Summary	Link
Python	✅ Success		View Check ↗
Test coverage	❌ Failure	❗ 1 occurence introduced 🚨 1 failing metric	View Check ↗

Code Coverage Report

Metric	Aggregate	Python
Branch Coverage	100%	100%
Composite Coverage	99.7%	99.7%
Line Coverage	99.7%	99.7%
New Branch Coverage	100%	100%
New Composite Coverage	66.7%	66.7%
New Line Coverage	66.7%, ❌ Below Threshold	66.7%, ❌ Below Threshold

---

💡 If you’re a repository administrator, you can configure the quality gates from the settings.