Add a new mandatory BooleanLiteralFolding pass which constant folds conditional branches with boolean literals as operands.
```
%1 = integer_literal -1
%2 = apply %bool_init(%1) // Bool.init(_builtinBooleanLiteral:)
%3 = struct_extract %2, #Bool._value
cond_br %3, bb1, bb2
```
->
```
...
br bb1
```
This pass is intended to run before DefiniteInitialization, where mandatory inlining and constant folding didn't run, yet (which would perform this kind of optimization).
This optimization is required to let DefiniteInitialization handle boolean literals correctly.
For example in infinite loops:
```
init() {
while true { // DI need to know that there is no loop exit from this while-statement
if some_condition {
member_field = init_value
break
}
}
}
```
Some places want to do in-order walks of MacroExpansionDecls, but still
visit auxiliary declarations. Rather than force them to specifically
filter out declarations from the MacroExpansionDecl, add a parameter to
visitAuxiliaryDecls to skip them.
