feat: add implicit native coercion constructor

[Jamison929611]

Which issue does this PR close?

• Closes Coercion::new_implicit is confusing when desired type is TypeSignatureClass::Native #24135.

Rationale for this change

When a coercion's desired type is a native logical type, callers currently have to repeat that type as both TypeSignatureClass::Native(...) and default_casted_type. This duplication is confusing and can allow the two values to disagree.

What changes are included in this PR?

• Add Coercion::new_implicit_native, which derives default_casted_type from the desired logical type and delegates to the existing new_implicit constructor.
• Keep Coercion::new_implicit unchanged for backward compatibility and non-native desired type classes.
• Migrate the representative reverse and approx_percentile_cont call sites linked from the issue.
• Update the Coercion rustdoc example and add a constructor-equivalence unit test.

Are these changes tested?

Yes:

• cargo test -p datafusion-expr-common test_new_implicit_native --lib
• cargo test -p datafusion-functions reverse --lib
• cargo test -p datafusion-functions-aggregate approx_percentile_cont --lib
• cargo test -p datafusion-expr-common --doc
• cargo clippy -p datafusion-expr-common -p datafusion-functions -p datafusion-functions-aggregate --all-targets --all-features -- -D warnings
• cargo fmt --all

The required full-workspace cargo clippy --all-targets --all-features -- -D warnings was also attempted on Windows. It reached an unrelated MSVC native-link failure while building protobuf-src (LNK2005/LNK4098 in protoc-gen-upb); affected-crate clippy passed with warnings denied, and CI will run the full Linux workspace checks.

No benchmark was run because this is an API convenience constructor that delegates to the existing constructor and does not change runtime execution.

Are there any user-facing changes?

Yes. This adds the public Coercion::new_implicit_native convenience API. It is additive and backward compatible; existing new_implicit callers continue to work unchanged.

[Jamison929611]

The substantive GitHub Actions workflows are currently marked action_required pending maintainer approval for this fork contributor. When convenient, could a maintainer approve the workflow runs? I'll monitor and address any resulting failures or review feedback.

[alamb]

FYI @Jefffrey you may be interested in this PR

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.28%. Comparing base (c08832d) to head (524966a).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #24282      +/-   ##
==========================================
- Coverage   81.29%   81.28%   -0.01%     
==========================================
  Files        1110     1110              
  Lines      385205   385223      +18     
  Branches   385205   385223      +18     
==========================================
+ Hits       313145   313147       +2     
- Misses      53580    53593      +13     
- Partials    18480    18483       +3     

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