RFR: 8372393: Document requirement for separate metallib installation with Xcode 26.1.1 [v2]

[Galder Zamarreño]

> Document the metal toolchain requirements starting with Xcode 26.

Galder Zamarreño has updated the pull request incrementally with one additional commit since the last revision:

  Fix line breaks

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Changes:
  - all: https://git.openjdk.org/jdk/pull/28489/files
  - new: https://git.openjdk.org/jdk/pull/28489/files/c9101083..427758b2

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28489&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28489&range=00-01

  Stats: 5 lines in 1 file changed: 1 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/28489.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28489/head:pull/28489

PR: https://git.openjdk.org/jdk/pull/28489