Refactor: Rename encodeBitmapToBase64Png to encodeBitmapToBase64Jpeg (#6905)

The private function `encodeBitmapToBase64Png` in
`firebase-vertexai/src/main/kotlin/com/google/firebase/vertexai/type/Part.kt`
was already compressing Bitmap images to JPEG format, not PNG.

This commit renames the function to `encodeBitmapToBase64Jpeg` to
accurately reflect its behavior. The single call site within the same
file has also been updated.

no-changelog

Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>

Author: rlazo

firebase-vertexai/src/main/kotlin/com/google/firebase/vertexai/type/Part.kt

@@ -171,7 +171,7 @@ internal fun Part.toInternal(): InternalPart {
     is TextPart -> TextPart.Internal(text)
     is ImagePart ->
       InlineDataPart.Internal(
-        InlineDataPart.Internal.InlineData("image/jpeg", encodeBitmapToBase64Png(image))
+        InlineDataPart.Internal.InlineData("image/jpeg", encodeBitmapToBase64Jpeg(image))
       )
     is InlineDataPart ->
       InlineDataPart.Internal(
@@ -193,7 +193,7 @@ internal fun Part.toInternal(): InternalPart {
   }
 }
 
-private fun encodeBitmapToBase64Png(input: Bitmap): String {
+private fun encodeBitmapToBase64Jpeg(input: Bitmap): String {
   ByteArrayOutputStream().let {
     input.compress(Bitmap.CompressFormat.JPEG, 80, it)
     return android.util.Base64.encodeToString(it.toByteArray(), BASE_64_FLAGS)