RFR: 8335911: Document ccls indexer in doc/ide.md

[Erik Joelsson]

On Mon, 8 Jul 2024 18:17:06 GMT, Volker Simonis <simonis at openjdk.org> wrote:

> `doc/ide.md` should also mention the [ccls indexer](https://github.com/MaskRay/ccls/wiki/Visual-Studio-Code).
> 
> Project files for it can be created by `make vscode-project-ccls`.

Marked as reviewed by erikj (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/20082#pullrequestreview-2165065561