Preparation for Internal/External residuals in PD

[lukelowry]

Description

Preparation for more general and capable model definitions. Co-simulation and EMT will benefit from this. It will also move toward agreement with PowerElectronics @alexander-novo

This is setup for issue #546 and PR #511

Proposed changes

• Temporarily rename evaluateInternalResidual to evaluateInternalResidualKernel
• Component function evaluateInternalResidual
• Component function evaluateExternalResidual

Checklist

• All tests pass.
• Code compiles cleanly with flags -Wall -Wpedantic -Wconversion -Wextra.
• The new code follows GridKit™ style guidelines.
• There are unit tests for the new code.
• N/A The new code is documented.
• The feature branch is rebased with respect to the target branch.
• N/A The CHANGELOG.md has been updated to reflect the changes. If this is a minor PR that is part of a larger fix already included in the file, state so.

Further comments

This eventually solves the component ordering issue, as the general order of system model's components should be

• readExternalVariables
• evaluateInternalResidual
• evaluateExternalResidual (e.g., inject current)