C#: Remove some unbounded TC computations

[hvitved]

We are in some cases computing (more or less) full non-fast TCs, which can be very expensive in cases like this one.

For example, the charpred of AstNode in ControlFlowGraphImpl.qll would previously result in the following DIL:

incremental
`#ControlFlowGraphImpl::getAChild/1#000c4110Plus#bf`(
  /* Element::Element */ interned entity p, /* Element::Element */ entity result
)
{
  [base_case]
  #@top_level_exprorstmt_parentMergeTypeCall(p) and
  `ControlFlowGraphImpl::getAChild/1#000c4110`(p, result)
  [recursive_case]
  exists(/* Element::Element */ entity mid |
    `ControlFlowGraphImpl::getAChild/1#000c4110`(mid, result) and
    delta previous rec `#ControlFlowGraphImpl::getAChild/1#000c4110Plus#bf`(p,
      mid)
  ) and
  not(
    previous rec `#ControlFlowGraphImpl::getAChild/1#000c4110Plus#bf`(p, result)
  )
}

suppressTypeErrors
ControlFlowGraphImpl::AstNode#QuickEval#27f9434f(
  /* ControlFlowGraphImpl::AstNode */ interned unique entity this
)
{
  (
    ControlFlowGraphImpl::TAstNode#636d28d6(this) and
    #@top_level_exprorstmt_parentMergeTypeCall(this) and
    not(#@attributeMergeTypeCall(this))
  )
  or
  exists(/* @top_level_exprorstmt_parent */ interned entity any#expr# |
    ControlFlowGraphImpl::TAstNode#636d28d6(this) and
    `#ControlFlowGraphImpl::getAChild/1#000c4110Plus#bf`(any#expr#, this) and
    #@top_level_exprorstmt_parentMergeTypeCall(any#expr#) and
    not(#@attributeMergeTypeCall(any#expr#))
  )
}

That is, we would compute a full TC only to afterwards filter away the target column via the any#expr#.