Fix regex syntax when pattern has double quote or escape on py and java

[fishcakez]

When trying to use regex patterns with quotes or escapes in there are syntax issues for py and java.

For py, the generated code for regex containing a " is not be escaped and fail at runtime with SyntaxError. Therefore reuse the python r usage handling so that Python converts to string to escape correctly. The test added will fail to compile without the fix:

[string - pattern (quote) - valid] (python harness) executor error: [tests/harness/python/python-harness tests/harness/python/python-harness] failed execution (exit status 1) - captured stderr:
Traceback (most recent call last):
  File "/tmp/bazel-working-directory/com_envoyproxy_protoc_gen_validate/bazel-out/aarch64-fastbuild/bin/tests/harness/executor/executor_python_test.runfiles/com_envoyproxy_protoc_gen_validate/tests/harness/python/harness.py", line 42, in <module>
    valid = validate(test_msg)
            ^^^^^^^^^^^^^^^^^^
  File "/tmp/bazel-working-directory/com_envoyproxy_protoc_gen_validate/bazel-out/aarch64-fastbuild/bin/tests/harness/executor/executor_python_test.runfiles/com_envoyproxy_protoc_gen_validate/python/protoc_gen_validate/validator.py", line 58, in validate
    return _validate_inner(ValidatingMessage(proto_message))(proto_message)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/bazel-working-directory/com_envoyproxy_protoc_gen_validate/bazel-out/aarch64-fastbuild/bin/tests/harness/executor/executor_python_test.runfiles/com_envoyproxy_protoc_gen_validate/python/protoc_gen_validate/validator.py", line 68, in _validate_inner
    exec(func, globals(), local_vars)
  File "<string>", line 7
    raise ValidationFailed("p.val pattern does not match ^[^"]*$")
                                                             ^
SyntaxError: closing parenthesis ']' does not match opening parenthesis '('
[string - pattern (quote) - invalid] (python harness) executor error: [tests/harness/python/python-harness tests/harness/python/python-harness] failed execution (exit status 1) - captured stderr:
Traceback (most recent call last):
  File "/tmp/bazel-working-directory/com_envoyproxy_protoc_gen_validate/bazel-out/aarch64-fastbuild/bin/tests/harness/executor/executor_python_test.runfiles/com_envoyproxy_protoc_gen_validate/tests/harness/python/harness.py", line 42, in <module>
    valid = validate(test_msg)
            ^^^^^^^^^^^^^^^^^^
  File "/tmp/bazel-working-directory/com_envoyproxy_protoc_gen_validate/bazel-out/aarch64-fastbuild/bin/tests/harness/executor/executor_python_test.runfiles/com_envoyproxy_protoc_gen_validate/python/protoc_gen_validate/validator.py", line 58, in validate
    return _validate_inner(ValidatingMessage(proto_message))(proto_message)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/bazel-working-directory/com_envoyproxy_protoc_gen_validate/bazel-out/aarch64-fastbuild/bin/tests/harness/executor/executor_python_test.runfiles/com_envoyproxy_protoc_gen_validate/python/protoc_gen_validate/validator.py", line 68, in _validate_inner
    exec(func, globals(), local_vars)
  File "<string>", line 7
    raise ValidationFailed("p.val pattern does not match ^[^"]*$")
                                                             ^
SyntaxError: closing parenthesis ']' does not match opening parenthesis '('

For java, the generated code for regex containing \ is not escaped and failed at compile. There is a commented out ReplaceAll for java to escape it. Removing the commented out line passes a simple text. Looking through the code history this commented out line has been there since original PR. The test added will fail to compile without the fix:

bazel-out/aarch64-fastbuild/bin/tests/harness/cases/_javac/java/libjava_tmp/tests/harness/cases/StringsValidator.java:320: error: ')' or ',' expected
		com.google.re2j.Pattern VAL__PATTERN = com.google.re2j.Pattern.compile("^[^\\"]*$");
		                                                                              ^
bazel-out/aarch64-fastbuild/bin/tests/harness/cases/_javac/java/libjava_tmp/tests/harness/cases/StringsValidator.java:320: error: unclosed string literal
		com.google.re2j.Pattern VAL__PATTERN = com.google.re2j.Pattern.compile("^[^\\"]*$");
		                                                                                 ^
bazel-out/aarch64-fastbuild/bin/tests/harness/cases/_javac/java/libjava_tmp/tests/harness/cases/StringsValidator.java:337: error: illegal escape character
		com.google.re2j.Pattern VAL__PATTERN = com.google.re2j.Pattern.compile("^\\\x41+$");