Hoist AbstractBufferedEncoder.position to a field when reading/writing it repeatedly.

This produces much better code for Android: https://godbolt.org/z/xE8T9xqrr

Down from 196 bytes to 140 bytes. Bounds checks get combined together.

This is a partial roll-forward of cl/673588324.

PiperOrigin-RevId: 681703327

java/core/src/main/java/com/google/protobuf/CodedOutputStream.java

diff --git a/java/core/src/main/java/com/google/protobuf/CodedOutputStream.java b/java/core/src/main/java/com/google/protobuf/CodedOutputStream.java
index 683f310..d3e7cc0 100644
--- a/java/core/src/main/java/com/google/protobuf/CodedOutputStream.java
+++ b/java/core/src/main/java/com/google/protobuf/CodedOutputStream.java
@@ -2365,10 +2365,12 @@
      * responsibility of the caller.
      */
     final void bufferFixed32NoTag(int value) {
+      int position = this.position; // Perf: hoist field to register to avoid load/stores.
       buffer[position++] = (byte) (value & 0xFF);
       buffer[position++] = (byte) ((value >> 8) & 0xFF);
       buffer[position++] = (byte) ((value >> 16) & 0xFF);
       buffer[position++] = (byte) ((value >> 24) & 0xFF);
+      this.position = position;
       totalBytesWritten += FIXED32_SIZE;
     }
 
@@ -2377,6 +2379,7 @@
      * responsibility of the caller.
      */
     final void bufferFixed64NoTag(long value) {
+      int position = this.position; // Perf: hoist field to register to avoid load/stores.
       buffer[position++] = (byte) (value & 0xFF);
       buffer[position++] = (byte) ((value >> 8) & 0xFF);
       buffer[position++] = (byte) ((value >> 16) & 0xFF);
@@ -2385,6 +2388,7 @@
       buffer[position++] = (byte) ((int) (value >> 40) & 0xFF);
       buffer[position++] = (byte) ((int) (value >> 48) & 0xFF);
       buffer[position++] = (byte) ((int) (value >> 56) & 0xFF);
+      this.position = position;
       totalBytesWritten += FIXED64_SIZE;
     }
   }