fix: correct ternary handling in java2spec, nullable strings in repeated elements

- java2spec: ternary with null false-branch (cond ? val : null) now
  preserves the original write method and uses the true branch as field
  name, instead of blindly treating all ternaries as bool-as-int.
  Fixes ClipData.ActivityInfo being misidentified as ParcelItemActivityInfos bool.

- codegen: string8/string16 in repeated elements are now *string with
  WriteNullableString/ReadNullableString, matching Java's nullable semantics.

- parcel: add WriteNullableString and WriteNullableString16 helpers.

- Revert unrelated codec2_test.go refactoring.

Author: xaionaro@dx.center

android/companion/virtual/virtualdeviceparams.go

@@ -52,6 +52,16 @@ func (p *Parcel) WriteNullString16() {
 	p.WriteInt32(-1)
 }
 
+// WriteNullableString16 writes a nullable string in UTF-16LE wire format.
+// If s is nil, writes a null sentinel (-1). Otherwise writes the string.
+func (p *Parcel) WriteNullableString16(s *string) {
+	if s == nil {
+		p.WriteNullString16()
+		return
+	}
+	p.WriteString16(*s)
+}
+
 // ReadString16 reads a string in UTF-16LE wire format.
 // Reads int32 char count. If -1, returns empty string.
 // Then reads (charCount+1)*2 bytes (including null terminator), padded to 4 bytes.
@@ -148,6 +158,16 @@ func (p *Parcel) WriteNullString() {
 	p.WriteInt32(-1)
 }
 
+// WriteNullableString writes a nullable string in UTF-8 wire format.
+// If s is nil, writes a null sentinel (-1). Otherwise writes the string.
+func (p *Parcel) WriteNullableString(s *string) {
+	if s == nil {
+		p.WriteNullString()
+		return
+	}
+	p.WriteString(*s)
+}
+
 // ReadString reads a string in UTF-8 wire format (for @utf8InCpp).
 // Reads int32 byte length. If -1, returns empty string.
 // Then reads byteLen+1 bytes (including null terminator), padded to 4 bytes.