swift234

SILGen: Fix static computed properties in protocol extensions

We need to keep the AST formal type of the base around when building up
lvalues.

When the getter or setter involves an accessor call, we would use the
lowered type of the self argument to form the call. However, it might be
at the wrong level of abstraction, causing a @thin -vs- @thick metatype
mismatch. Using the formal type instead allows SILGenApply logic to emit
a thin to thick metatype conversion if necessary.

Fixes <rdar://problem/21358641>.

Swift SVN r30913