Initcap behaves differently in Spark and in DataFusion (also Comet)

[Blizzara]

Describe the bug

DataFusion's initcap behaves differently than Spark's. While both do "upper-case the first letter of each word and lowercase others", Spark considers as words anything separated by whitespace (' '), while DataFusion considers anything separated by non-ascii-alphanumeric as words. (DF's code would also fail to uppercase or lowercase non-ascii chars, but that doesn't materialize as a separate issue as it considers them separators already in the first place.)

#1051 shows the problem by adding two cases to the test, one using a dash and one using non-ascii letters (from Finnish).

== Results ==
!== Correct Answer - 7 ==       == Spark Answer - 7 ==
 struct<initcap(name):string>   struct<initcap(name):string>
 [James Smith]                  [James Smith]
 [James Smith]                  [James Smith]
![James Ähtäri]                 [James äHtäRi]
 [Michael Rose]                 [Michael Rose]
 [Rames Rose]                   [Rames Rose]
![Robert Rose-smith]            [Robert Rose-Smith]
 [Robert Williams]              [Robert Williams]

Steps to reproduce

Call initcap with an input containing non-ascii-alphanumeric non-whitespace characters

Expected behavior

Match Spark

Additional context

No response

[viirya]

Thanks for reporting this bug.