chore(functions): fix function names typo

[appletreeisyellow]

Which issue does this PR close?

This is a followup PR for #7262. No related issue.

Rationale for this change

I found typos in function names that will printout in error message:

• regex_replace should be regexp_replace
• rtrimp should be rtrim

DataFusion CLI v23.0.0
❯ SELECT regexp_replace(arrow_cast('foobar', 'Dictionary(Int32, Utf8)'), 'bar', 'xx', 'gi');
Internal error: The "regex_replace" function can only accept strings.. This was likely caused by a bug in DataFusion's code and we would welcome that you file an bug report in our issue tracker
                         ^
❯ SELECT rtrim(arrow_cast(' foo ', 'Dictionary(Int32, Utf8)'));
Internal error: The "rtrimp" function can only accept strings.. This was likely caused by a bug in DataFusion's code and we would welcome that you file an bug report in our issue tracker
                          ^

What changes are included in this PR?

Fix typos

Are these changes tested?

Tested manually, there is no logic change in this PR

Are there any user-facing changes?

Users will see the correct function names in the error messages for regexp_replace and rtrim

[alamb]

Nice find -- thank you @appletreeisyellow !