This implements a number of new safety checks and error messages
when object constructors are used:
In case objects:
* the compiler will prevent you from initializing fields in
conflicting branches
* When a field from a particular branch is initialized, the
compiler will demand that the discriminator field is also
supplied with a maching compile-time value
In all objects:
* When the "requiresInit" pragma is applied to a type, all fields
of the type must be initialized when object construction is used.
The code will be simplified in a follow up commit.
properly disabling the extra diagnostics in semCompiles proved to
be too much work. I have some plans for further improving the error
messages in the future and I'll revisit this later.
Fixed the dot operator when used within return types (see tgenericdotrettype)
Fixed the matching of generic concepts aliases used with the implicit generics style
* Why is tyInferred needed?
The bindings in TCandidate are capable of inferring types within a single
call expression. In concepts, we need to infer types in the same way, but
across the whole body of the concept.
Previously, once a concept type param was inferred, it was destructively
mutated using t.assignType, but this proved to be problematic in the presence
of overloads, because the bindings established while a non-matching overload
is tested must be reverted/forgotten. tyInferred offers a non-destructive way to
keep track of the inference progress.
While introducing new types usually requires a lot of code paths in the compiler
to updated, currently tyInferred is only a short-lived type within the concept body
pass and it's unlikely to introduce breakage elsewhere in the compiler.
