[foreign-abi] RFR: 8253373: Add package-level javadoc for foreign linker support [v2]

[Maurizio Cimadamore]

> This patch modifies the toplevel javadoc of jdk.incubator.foreign to add details about the ABI support.
> 
> I've decided to split the javadoc into two main sections - one about memory access, and one about foreign function
> access; they have subsections for more detailed info.
> There's also a trailing toplevel section on "restricted method". I'm still wordsmithing the definition of "what's it
> like to be a restricted method" together with Alex, but this is a first attempt. It is likely that, once we have this
> done, we can have the various restrcited definitions inside the API refer bakc to this section.
> Link to javadoc:
> http://cr.openjdk.java.net/~mcimadamore/panama/foreign-linker-javadoc/javadoc/jdk/incubator/foreign/package-summary.html

Maurizio Cimadamore has updated the pull request incrementally with five additional commits since the last revision:

 - Update src/jdk.incubator.foreign/share/classes/jdk/incubator/foreign/package-info.java
   
   Co-authored-by: Jorn Vernee <JornVernee at users.noreply.github.com>
 - Update src/jdk.incubator.foreign/share/classes/jdk/incubator/foreign/package-info.java
   
   Co-authored-by: Jorn Vernee <JornVernee at users.noreply.github.com>
 - Update src/jdk.incubator.foreign/share/classes/jdk/incubator/foreign/package-info.java
   
   Co-authored-by: Jorn Vernee <JornVernee at users.noreply.github.com>
 - Update src/jdk.incubator.foreign/share/classes/jdk/incubator/foreign/package-info.java
   
   Co-authored-by: Jorn Vernee <JornVernee at users.noreply.github.com>
 - Update src/jdk.incubator.foreign/share/classes/jdk/incubator/foreign/package-info.java
   
   Co-authored-by: Jorn Vernee <JornVernee at users.noreply.github.com>

-------------

Changes:
  - all: https://git.openjdk.java.net/panama-foreign/pull/346/files
  - new: https://git.openjdk.java.net/panama-foreign/pull/346/files/eb09b53f..4b21814e

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=346&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=346&range=00-01

  Stats: 7 lines in 1 file changed: 2 ins; 0 del; 5 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/346.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/346/head:pull/346

PR: https://git.openjdk.java.net/panama-foreign/pull/346