RFR: JDK-8305004: add @spec tags to langtools modules

[Iris Clark]

On Tue, 28 Mar 2023 02:26:49 GMT, Jonathan Gibbons <jjg at openjdk.org> wrote:

> Please review a simple doc-only PR to add `@spec` tags to 3 "langtools" modules, for eventual use in an "External Specifications" page.

Marked as reviewed by iris (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/13201#pullrequestreview-1360128468