Rename sem_*.cc to *.cc

This makes the .cc files match the header file name, which allows for
the text editor "header flip" feature to actually work. The reason these
files were named this way was because GN doesn't allow name conflicts in
the same source set, despite the files being in different directories.
This change splits the files into different source sets. To do so, we
use GN templates, which also reduces duplication in each target
definition.

Bug: tint:724
Change-Id: I9a7ed3912e4b85b2b38d360805203f3488b86c4c
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/48160
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Antonio Maiorano <amaiorano@google.com>

src/sem/member_accessor_expression.cc

@@ -15,6 +15,8 @@
 #include "src/ast/member_accessor_expression.h"
 #include "src/sem/member_accessor_expression.h"
 
+#include <utility>
+
 TINT_INSTANTIATE_TYPEINFO(tint::sem::MemberAccessorExpression);
 TINT_INSTANTIATE_TYPEINFO(tint::sem::StructMemberAccess);
 TINT_INSTANTIATE_TYPEINFO(tint::sem::Swizzle);

src/sem/struct.cc

@@ -12,8 +12,10 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-#include "src/ast/struct_member.h"
 #include "src/sem/struct.h"
+#include "src/ast/struct_member.h"
+
+#include <utility>
 
 TINT_INSTANTIATE_TYPEINFO(tint::sem::Struct);
 TINT_INSTANTIATE_TYPEINFO(tint::sem::StructMember);

src/sem/struct.h

@@ -22,6 +22,7 @@
 
 #include "src/ast/storage_class.h"
 #include "src/sem/node.h"
+#include "src/symbol.h"
 
 namespace tint {