Added bare functions to values clause

[WittierDinosaur]

Brief summary of the change made

Bugfix PR for bare functions not being accepted in a VALUES clause
Fixes #1875

Are there any other side effects of this change that we should be aware of?

No

Pull Request checklist

Test case added in Postgres - to match bug report

[codecov]

Codecov Report

Merging #1876 (4f19310) into main (8d7ff64) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##              main     #1876   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          139       139           
  Lines         9880      9880           
=========================================
  Hits          9880      9880           

Impacted Files	Coverage Δ
src/sqlfluff/dialects/dialect_ansi.py	100.00% <ø> (ø)

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