[foreign-preview] RFR: 8282805: Javadoc for restricted method does not reflect updates to --enable-native-access

[Maurizio Cimadamore]

This simple patch updates the javadoc comments for restricted methods to reflect the updated behavior of the `--enable-native-access` flag.
All the `@throws` tags in restricted methods are updated, as well as the toplevel package javadoc section on restricted methods.

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Commit messages:
 - Initial push

Changes: https://git.openjdk.java.net/panama-foreign/pull/665/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=665&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8282805
  Stats: 42 lines in 5 files changed: 3 ins; 0 del; 39 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/665.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/665/head:pull/665

PR: https://git.openjdk.java.net/panama-foreign/pull/665