[pkg/ottl] Add new ottl.ValueComparator API and support for slices comparison

[edmocosta]

Description

This PR introduces two related changes and contains 2 change logs because of that.

1 - Comparator API

Exposes the internal OTTL comparators logic as a new API (ottl.ValueComparator), which can be used by API consumers to compare raw values following the same OTTL comparison rules .

Why?

Existing and new functions that needs to compare values can be leveraging this new API to compare them, and keep it consistent with the OTTL comparison logic. For example, the new Contains function for slices, can be using this API to determine whether an slice contains a particular value, following the same comparison logic the grammar does.

// Exported interface:
type ValueComparator interface {
	// Equal compares two values for equality, returning true if they are equals
	// according to the OTTL comparison rules.
	Equal(a any, b any) bool
	// NotEqual compares two values for equality, returning true if they are different
	// according to the OTTL comparison rules.
	NotEqual(a any, b any) bool
	// Less compares two values, returning true if the first value is less than the second
	// value, using the OTTL comparison rules.
	Less(a any, b any) bool
	// LessEqual compares two values, returning true if the first value is less or equal
	// to the second value, using the OTTL comparison rules.
	LessEqual(a any, b any) bool
	// Greater compares two values, returning true if the first value is greater than the
	// second value, using the OTTL comparison rules.
	Greater(a any, b any) bool
	// GreaterEqual compares two values, returning true if the first value is greater or
	// equal to the second value, using the OTTL comparison rules.
	GreaterEqual(a any, b any) bool
}

// Usage:
comp := ottl.NewValueComparator()

2 - Add ability to compare slices

We currently don't have the ability to compare slices, which means conditions like attributes["slice"] == attributes["slice"] returns false. This PR also adds the ability to compare slices/pcommon.Slices, similar to the maps support (#38611).

Testing

Manual and unit tests

Documentation

Updated LANGUAGE.md

[TylerHelmuth]

Can you add the var _ = (ValueComparator)(nil) thing that enforces this type is a ValueComparator?

[edmocosta]

I think in this case we probably don't need that, the NewValueComparator() ValueComparator { return &ottlValueComparator{} } is already ensuring it, if ottlValueComparator does not satisfy the interface, compilation would break.

[evan-bradley]

I'm okay either way here, I don't think we gain or lose much by adding it since NewValueComparator implicitly does this check.