EntityId: Soft-deprecate Serializable methods and stop using them

Most callers of serialize() should use getSerialization() instead (tests
for the method specifically are left alone for now); unserialize()
doesn’t even have any callers outside of its tests and __unserialize()
ipmlementations.

While it was never guaranteed that serialize() and getSerialization()
return the same string, this is indeed the case for all EntityId classes
I could find, and a lot of the callers were relying on it anyway.

Bug: T345856
Change-Id: I64e2e54b344e8dd64078f81502d0d067f6ea3a5b

Author: lucaswerkmeister

src/Entity/EntityId.php

@@ -32,6 +32,21 @@ public function __toString();
 	 */
 	public function equals( $target );
 
+	/**
+	 * @see Serializable::serialize()
+	 * @return string|null
+	 * @deprecated Use {@link self::getSerialization()} instead.
+	 */
+	public function serialize();
+
+	/**
+	 * @see Serializable::unserialize()
+	 * @param string $data
+	 * @return void
+	 * @deprecated There should be no reason to use this.
+	 */
+	public function unserialize( $data );
+
 	/**
 	 * This method replaces {@link Serializable::serialize()}.
 	 * Do not call it manually.

src/Entity/EntityIdValue.php

@@ -37,7 +37,7 @@ public function getHash(): string {
 	 * @return string
 	 */
 	public function getSerializationForHash(): string {
-		$data = $this->entityId->serialize();
+		$data = $this->entityId->getSerialization();
 		$innerSerialization = 'C:' . strlen( get_class( $this->entityId ) ) . ':"' . get_class( $this->entityId ) .
 		'":' . strlen( $data ) . ':{' . $data . '}';