[C++] Rename arrow::util::StringBuilder and move to internal namespace

[amoeba]

Describe the enhancement requested

During review of #46180, it came up that Arrow C++ has two StringBuilders:

1. The public builder for utf8() arrays, https://github.com/apache/arrow/blob/main/cpp/src/arrow/array/builder_binary.h#L424 (class)
2. A helper in https://github.com/apache/arrow/blob/main/cpp/src/arrow/util/string_builder.h (function)

We should,

• Move StringBuilder (2) in cpp/src/arrow/util/string_builder.h from arrow::util to arrow::internal to make its intended use more clear
• Rename arrow/util/string_builder.{h,c} and arrow::util::StringBuilder to something else to avoid confusing humans and computers

No changes would be made to the official Arrow StringBuilder class.

Component(s)

C++

[bkietz]

It's worth noting that arrow::util::StringBuilderRecursive() (and possibly arrow::util::StringBuilder itself) is a helper function which is no longer necessary in C++17 at all; we can use fold expressions to achieve the same result:

 template <typename... Args>
 static Status FromArgs(StatusCode code, const Args&... args) {
 std::stringstream ss;
 (ss << ... << args);
 return Status(code, ss.str());
 }

[pitrou]

@amoeba Would you like to tackle this issue?

[Ziy1-Tan]

take

[pitrou]

Issue resolved by pull request 46813
#46813