[b/441876236] Refactor: don't "partially format" in Assessment flow

[misolt]

This is the first step of a refactor, which is meant to simplify how the queries are built for assessment.

Change the flow of assessment to avoid the partial-substitution trick while creating tasks:

String overrideWhere = arguments.getDefinition(propertyWhere);
if (overrideWhere != null) {
  // Partially format the SQL template by re-introducing the first format specifier.
  return String.format(defaultSql, "%1$s", " WHERE " + overrideWhere);
}

Instead, apply both substitutions in a single step (using AssessmentQuery#substitute).