Update Psalm to 3.17.2 and lock the version used with GitHub Actions

Bump Psalm level to 3

Rename Comparator::diffTable() params - from/to instead of 1/2

Migrate jobs away from Travis to Github Actions 

Minor CS improvement - use ::class for TestCase::expectException input

It should be faster, and will result in one fewer CI platform to
maintain.

Add Statement::fetchAllIndexedAssociative() and ::iterateIndexedAssociative()

Static analysis workflow

It is more concise.

The end goal is to have a generic workflow that can be contributed back
to our .github repository.

I somehow missed another occurrence.

When we push to a branch on origin and make a PR, we see double the
normal amount of jobs because of this.

Modernize existing ga