Rename some symbols related to pointers types (#8592)

Note that while this change touched a large numer of files, there are no
changes to functionality being made here. The only things being done are
renaming various symbols and, in a few cases, updating or adding
comments for consistency with the new names.

The core of the naming changes are:

* Most things named to refer to `OutType` (e.g., `IROutType`,
`IRBuilder::getOutType()`, etc.) have been consistently renamed to refer
to `OutParamType`, to emphasize that the relevant AST/IR node types are
only intended for use to represent `out` parameters.

* The same change as described above for `OutType` is also made for
`RefType`, which becomes `RefParamType` in most cases. One mess that
this exposes is the way that the `ExplicitRef<T>` type in the core
module currently lowers to `IRRefParamType`. This change sticks to the
rule of not making functional changes, so that mess is left as-is for
now.

* Names referring to `InOutType` have been changed to instead refer to
`BorrowInOutType`. The intention with this naming change is to emphasize
that the Slang rules for `inout` are semantically those of a borrow (or
at least our interpretation of what a borrow means).

* Names referring to `ConstRefType` have been changed to instead refer
to `BorrowInType`. This change starts work on clarifying that the
existing `__constref` modifier was never intended to be a read-only
analogue of `__ref`, and instead is the input-only analogue of `inout`.

* The `ParameterDirection` enum type has been changed to
`ParamPassingMode`, to reflect the fact that the concept of "direction"
fails to capture what is actually being encoded, particularly once we
have modes beyond simple `in`/`out`/`inout`.

While this change does not alter behavior in any case (the user-exposed
Slang language is unchanged), it is intended to set up subsequence
changes that will work to make the handling of these types in the
compiler more nuanced and correct. Breaking this part of the change out
separately is primarily motivated by a desire to minimize the effort for
reviewers.

---------

Co-authored-by: slangbot <186143334+slangbot@users.noreply.github.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/tests/diagnostics/const-ref-differentiable-param.slang b/tests/diagnostics/const-ref-differentiable-param.slang
index c345826e7..354744701 100644
--- a/tests/diagnostics/const-ref-differentiable-param.slang
+++ b/tests/diagnostics/const-ref-differentiable-param.slang
@@ -32,7 +32,7 @@ struct MyType2
     float compute1(float x) { return 0; }
 }
 
-// CHECK-DAG: {{.*}}(5): error 38034: cannot use '__constref' on a differentiable parameter.
+// CHECK-DAG: {{.*}}(5): error 38034: cannot use 'borrow in' on a differentiable parameter.
 // CHECK-NOT {{.*}}error
 // CHECK-DAG: {{.*}}(14): error 38034: cannot use '[constref]' on a differentiable member method of a differentiable type.
 // CHECK-NOT {{.*}}error