[SPARK-48693][SQL] Simplify and unify toString of Invoke and StaticInvoke

[yaooqinn]

What changes were proposed in this pull request?

The StaticInvoke class is used extensively by RuntimeReplacable expressions, due to its ugly string representation, a plan with multiple or nested StaticInvoke is hard to read.

This PR overrides StaticInvoke's toString method to improve its readability.

 Project [left(c7#x, 2) AS left(c7, 2)#x, left(c8#x, 2) AS left(c8, 2)#x, left(v#x, 3) AS left(v, 3)#x, left(s#x, 2) AS left(s, 2)#x]
 +- SubqueryAlias spark_catalog.default.char_tbl4
-   +- Project [staticinvoke(class org.apache.spark.sql.catalyst.util.CharVarcharCodegenUtils, StringType, readSidePadding, c7#x, 7, tru
e, false, true) AS c7#x, staticinvoke(class org.apache.spark.sql.catalyst.util.CharVarcharCodegenUtils, StringType, readSidePadding, c8#
x, 8, true, false, true) AS c8#x, v#x, s#x]
+   +- Project [static_invoke(CharVarcharCodegenUtils.readSidePadding(c7#x, 7)) AS c7#x, static_invoke(CharVarcharCodegenUtils.readSideP
adding(c8#x, 8)) AS c8#x, v#x, s#x]

In contrast, the Invoke's toString is overly simple, losing its child's string representations.

Why are the changes needed?

improve plan readability and consistency

Does this PR introduce any user-facing change?

Yes, a plan containing StaticInvoke will change its string representation.

How was this patch tested?

existing modified tests

Was this patch authored or co-authored using generative AI tooling?

no

[yaooqinn]

cc @cloud-fan @LuciferYang @dongjoon-hyun @HyukjinKwon thanks

[yaooqinn]

Merged to master, thank you all.