CodeElement ancestor functionality

[PaulSandoz]

Declare common ancestor methods on CodeElement.

This enables more uniform traversal up the tree of code elements and querying of ancestors.

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Progress

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Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/babylon.git pull/479/head:pull/479
$ git checkout pull/479

Update a local copy of the PR:
$ git checkout pull/479
$ git pull https://git.openjdk.org/babylon.git pull/479/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 479

View PR using the GUI difftool:
$ git pr show -t 479

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/babylon/pull/479.diff

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[openjdk]

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See the Progress checklist in the description for automated requirements.