tint: intrinsics.def Support [[precedence]] decoration

Add support for a [[precedence(N)]] decoration on intrinsic table type
declarations. This will be used to ensure the type with the lowest
conversion rank is matched when a matcher could match multiple types
for a given abstract numeric argument type.

Bug: tint:1504
Change-Id: I96475b000c0917bbfa4e2873b1731ce048b96a7d
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/90664
Reviewed-by: David Neto <dneto@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>

tools/src/cmd/intrinsic-gen/sem/sem.go

@@ -16,6 +16,7 @@ package sem
 
 import (
 	"fmt"
+	"sort"
 
 	"dawn.googlesource.com/dawn/tools/src/cmd/intrinsic-gen/ast"
 )
@@ -89,6 +90,7 @@ type Type struct {
 	Decl           ast.TypeDecl
 	Name           string
 	DisplayName    string
+	Precedence     int
 }
 
 // TypeMatcher declares a type matcher
@@ -99,6 +101,13 @@ type TypeMatcher struct {
 	Types          []*Type
 }
 
+func (t TypeMatcher) PrecedenceSortedTypes() []*Type {
+	out := make([]*Type, len(t.Types))
+	copy(out, t.Types)
+	sort.Slice(out, func(i, j int) bool { return out[i].Precedence > out[j].Precedence })
+	return out
+}
+
 // EnumMatcher declares a enum matcher
 type EnumMatcher struct {
 	TemplateParams []TemplateParam