Fix false negatives in analysis of do/while loops

Follow up to https://github.com/phan/phan/issues/2026

I really should redesign parts of this to be a completely accurate version of a definition-use graph instead of a mostly accurate version if I want to fix every edge case for do-while.

• Also known as a use-define chain : https://en.wikipedia.org/wiki/Use-define_chain
• As part of this change, this should also treat break as going to a different node than continue
• Some statements are not Nodes, will need to handle this (e.g. ;2;). Creating empty ast\Node to mark blocks in the def-use graph is one way to do that.
• Will need to refactor this to track definitions in a more generic way. (just check if it's possible to have any definition outside of a block of code instead of the current approach of tracking the specific definitions. The current approach does not work well with loops).

It'd also help in the long run if I wrote tools to represent a tool to convert the resulting definitions and usages generated by this plugin to a graph (e.g. dot file https://www.graphviz.org/doc/info/lang.html) for internal usages

• This graph be used when debugging with graphviz as a visualizer; unit tests can verify that the resulting graphs are accurate and avoid regressions when fixing any other issues
• If there are 3 ast\Nodes on line 7, then label the first one L7N1, the second one L7N2, etc (Some nodes will have the same column and we don't track the column).

https://github.com/phan/phan/blob/master/src/Phan/Plugin/Internal/VariableTrackerPlugin.php
https://github.com/phan/phan/tree/master/src/Phan/Plugin/Internal/VariableTracker

examples of a false positive/negative caused by break/continue - E.g. the variable is defined before a break so it isn't used within the loop, the variable is defined before a break so it isn't used within the condition, etc.

Start with src/Phan/Plugin/Internal/VariableTrackerPlugin.php and the files under src/Phan/Plugin/Internal/VariableTracker, then review issue 2026 for the do/while context. The work involves making the definition-use graph accurate for do/while control flow, distinguishing break from continue, and handling statements that are not Nodes. Done would include regression coverage for the reported false positives and negatives; graph visualization and labeling are suggested longer-term tooling.