[clang][dataflow] Simplify flow conditions displayed in HTMLLogger. (#70848)

This can make the flow condition significantly easier to interpret; see
below
for an example.

I had hoped that adding the simplification as a preprocessing step
before the
SAT solver (in `DataflowAnalysisContext::querySolver()`) would also
speed up SAT
solving and maybe even eliminate SAT solver timeouts, but in my testing,
this
actually turns out to be a pessimization. It appears that these
simplifications
are easy enough for the SAT solver to perform itself.

Nevertheless, the improvement in debugging alone makes this a worthwhile
change.

Example of flow condition output with these changes:

```
Flow condition token: V37
Constraints:
(V16 = (((V15 & (V19 = V12)) & V22) & V25))
(V15 = ((V12 & ((V14 = V9) | (V14 = V4))) & (V13 = V14)))
True atoms: (V0, V1, V2, V5, V6, V7, V29, V30, V32, V34, V35, V37)
False atoms: (V3, V8, V17)
Equivalent atoms:
(V11, V15)

Flow condition constraints before simplification:
V37
((!V3 & !V8) & !V...