Add useful factory methods for ToolchainTypeRequirement.

Part of Optional Toolchains (#14726).

Closes #14825.

PiperOrigin-RevId: 428865799

src/main/java/com/google/devtools/build/lib/analysis/config/ToolchainTypeRequirement.java

@@ -19,6 +19,17 @@
 /** Describes a requirement on a specific toolchain type. */
 @AutoValue
 public abstract class ToolchainTypeRequirement {
+
+  /** Returns a new {@link ToolchainTypeRequirement}. */
+  public static ToolchainTypeRequirement create(Label toolchainType) {
+    return builder(toolchainType).build();
+  }
+
+  /** Returns a builder for a new {@link ToolchainTypeRequirement}. */
+  public static Builder builder(Label toolchainType) {
+    return builder().toolchainType(toolchainType);
+  }
+
   /** Returns a builder for a new {@link ToolchainTypeRequirement}. */
   public static Builder builder() {
     return new AutoValue_ToolchainTypeRequirement.Builder().mandatory(true);

src/main/java/com/google/devtools/build/lib/packages/ExecGroup.java

@@ -88,7 +88,7 @@ public interface Builder {
     default Builder requiredToolchains(ImmutableSet<Label> toolchainTypes) {
       ImmutableSet<ToolchainTypeRequirement> toolchainTypeRequirements =
           toolchainTypes.stream()
-              .map(label -> ToolchainTypeRequirement.builder().toolchainType(label).build())
+              .map(label -> ToolchainTypeRequirement.create(label))
               .collect(toImmutableSet());
       return this.toolchainTypes(toolchainTypeRequirements);
     }

src/main/java/com/google/devtools/build/lib/skyframe/ToolchainContextKey.java

@@ -69,7 +69,7 @@ default Builder requiredToolchainTypeLabels(Label... requiredToolchainTypeLabels
     default Builder requiredToolchainTypeLabels(ImmutableSet<Label> requiredToolchainTypeLabels) {
       ImmutableSet<ToolchainTypeRequirement> toolchainTypeRequirements =
           requiredToolchainTypeLabels.stream()
-              .map(label -> ToolchainTypeRequirement.builder().toolchainType(label).build())
+              .map(label -> ToolchainTypeRequirement.create(label))
               .collect(toImmutableSet());
       return this.toolchainTypes(toolchainTypeRequirements);
     }