Enable more IntelliJ inspections (#2827)

* Enable many more IntelliJ inspections

## Motivation

We recently created a repository-wide, project-level inspection profile,
which allows us to share and synchronize the inspections used across all
contributors. This works well, but the inspection profile we created was
based on the IntelliJ defaults, which is intentionally conservative
(i.e., does not enable most inspections). We should take advantage of
more of the very helpful inspections that IntelliJ offers, since they
can help improve code quality, and IntelliJ's static analysis recognizes
many issues that SonarQube does not.

## Modifications

This change enables most inspections that I personally feel offer value,
as well as setting them to the severity-level (i.e. weak vs strong
warning) that I personally feel is appropriate. Whether an inspection
offers value is obviously highly subjective, but this change allows us
to bias towards increasing our overall visibility to potential issues.
Over time, if we feel certain inspections do not offer value, we can
then selectively tune or disable those.

Author: Bennett-Lynch