[CALCITE-6313] Add POWER function for PostgreSQL

[normanj-bitquill]

• The existing power function is moved to all non PostgreSQL libraries
• The new power function is only for PostgreSQL
• The new function returns a decimal if any argument is a decimal

[normanj-bitquill]

In order to separate the POWER function for PostgreSQL and non-PostgreSQL dialects, the POWER function was moved to the SqlLibraryOperators class. This downgrades the POWER function from a standard function to a function from a library. This is problematic for things like SQRT which is a standard function and gets rewritten to a POWER expression.

Is there a more clean way to separate the POWER function so that the PostgreSQL implementation is able to return Decimal values in some cases?

[mihaibudiu]

In general, until the changes are approved I would recommend adding new commits instead of force-pushing. It makes it easier for reviewers to see what's new. Then you can squash when the PR is approved.

[sonarqubecloud[bot]]

Quality Gate passed

Issues
3 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud