chore: migrate build scripts to Gradle

[vlsi]

Checklist

Build

• gettext
• Support Java 7
• Build postgresql.jar (ensure shaded jar is published)
• Add OSGi manifest entries
• https://repo1.maven.org/maven2/org/postgresql/postgresql/42.2.10/postgresql-42.2.10-features.xml
• Support "skip scram", "skip waffle", "skip osgi" options
• Fedora build
• Fix CI scripts
• Add GitHub Actions
• remove pom.xml from Git control
• bring ubenchmark back

Testing

• Use JUnit 5 for test execution
• SSL tests
• Replication tests
• Test coverage

Release

Release is handled with https://github.com/vlsi/vlsi-release-plugins/tree/master/plugins/stage-vote-release-plugin (which has already been tested for https://github.com/autostyle/autostyle)

• Align license management for third-party: https://gitlab.com/ongresinc/scram/issues/11
• Publish Maven to Maven Central
• Create a source distribution
• Release approach (e.g. git tag, publish, etc)

Other

• Update documentation
• Findbugs/Spotbugs? Is it required?
• Publish results to Sonar

[vlsi]

It turns out InsertRewriteWithAlternatingTypesIssue584 was never executed since it was never included in a test suite.

@Chrriis , I'm inclined to drop the test as it is hard to understand what the test is doing.

The failure is as in https://travis-ci.org/pgjdbc/pgjdbc/jobs/618473901#L857

org.postgresql.jdbc.InsertRewriteWithAlternatingTypesIssue584 > testPreparedStatementPreparation[insertRewrite = true] FAILED
    org.junit.ComparisonFailure: expected:<S_[1]> but was:<S_[45]>
        at org.junit.Assert.assertEquals(Assert.java:115)
        at org.junit.Assert.assertEquals(Assert.java:144)
        at org.postgresql.jdbc.InsertRewriteWithAlternatingTypesIssue584.testPreparedStatementPreparation(InsertRewriteWithAlternatingTypesIssue584.java:133)

[davecramer]

@vlsi congrats! first smoke test passed