tpl/collections: Fix apply to work with built-in funcs like len

[bep]

Fixes #13418

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[Copilot]

Pull request overview

This PR fixes issue #13418 by enabling the apply function to work with Go's built-in template functions like len and not, which expect reflect.Value arguments. The fix adds logic to automatically wrap arguments in reflect.Value when the target function requires it.

• Adds automatic argument wrapping for built-in functions that expect reflect.Value parameters
• Introduces a package-level variable to cache the reflect.Type of reflect.Value
• Adds integration test to verify len and not work correctly with apply

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
tpl/collections/apply.go	Adds typeOfReflectValue variable and wrapping logic in applyFnToThis to convert arguments to reflect.Value when required by built-in template functions
tpl/collections/collections_integration_test.go	Adds TestApplyBuiltInIssue13418 test to verify apply works with built-in functions len and not

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[Copilot]

The wrapping logic only processes non-variadic parameters (iterating up to num). For variadic built-in functions like index or slice that take ...reflect.Value parameters, the variadic arguments won't be wrapped. Consider extending the loop to also wrap variadic parameters by checking if fn.Type().IsVariadic() and then wrapping arguments at indices >= num using fn.Type().In(num) as the expected type.

[Copilot]

Grammar issue: "funcs" is plural, so the verb should be "use" instead of "uses".

Suggested change

	// Go's built-in template funcs (e.g. len) uses reflect.Value as argument type.
	// Go's built-in template funcs (e.g. len) use reflect.Value as argument type.