GH-47230: [C++] Fixes C++23 compatibility issues

[ryanvo504]

Rationale for this change

This change improves compilation times and supports C++23 compatibility.

What changes are included in this PR?

Moves constructor, move constructor, move assignment operator, and member function implementations (Find, CreateEntry, AssignEntry, DeleteEntry) from inline definitions in the header to the source file. Also fixes duplicate "public:" access specifier in Entry class.

Are these changes tested?

Are there any user-facing changes?

Closes #47230

[github-actions]

Thanks for opening a pull request!

If this is not a minor PR. Could you open an issue for this pull request on GitHub? https://github.com/apache/arrow/issues/new/choose

Opening GitHub issues ahead of time contributes to the Openness of the Apache Arrow project.

Then could you also rename the pull request title in the following format?

GH-${GITHUB_ISSUE_ID}: [${COMPONENT}] ${SUMMARY}

or

MINOR: [${COMPONENT}] ${SUMMARY}

See also:

• Other pull requests
• Contribution Guidelines - Contributing Overview

[kou]

We need to work on #47208 before this.

[kou]

Could you rebase on main to use #47261 and #47318 ?