See https://github.com/googleapis/google-cloud-php/issues/9193
`protoc` is generating the invalid class name `Object` when it should be prefixed with `PB` to prevent a conflict with PHP reserved words. I've submitted a fix for this in #27475
This PR introduces the script `php/update_reserved_words.sh` which updates the library in the **8 different classfiles** which all have various ways this logic is defined. Hopefully this makes these things easier for us to maintain in the future.
**NOTE**: prefixing constants with PB has been unnecessary since PHP 7, so we can and should open those up to every word but `class` in the next major version. I've added a comment so we (hopefully) don't forget
```sh
$ bash php/update_reserved_words.sh
Updated src/google/protobuf/compiler/php/names.cc
Updated php/ext/google/protobuf/names.c
Updated src/google/protobuf/compiler/php/php_generator.cc
Updated php/tests/proto/test_reserved_message_lower.proto
Updated php/tests/proto/test_reserved_message_upper.proto
Updated php/tests/proto/test_reserved_enum_lower.proto
Updated php/tests/proto/test_reserved_enum_upper.proto
Updated php/tests/proto/test_reserved_enum_value_lower.proto
Updated php/tests/proto/test_reserved_enum_value_upper.proto
Updated php/tests/GeneratedClassTest.php
Updated php/src/Google/Protobuf/Internal/GPBUtil.php
```
Closes#27456
COPYBARA_INTEGRATE_REVIEW=https://github.com/protocolbuffers/protobuf/pull/27456 from bshaffer:php-update-reserved-words 522d93f1c1
PiperOrigin-RevId: 962903274
