[jdk21u-dev] RFR: 8305814: Backport b1625af600

[Ryan Flegel]

This is a backport of [JDK-8305814](https://bugs.openjdk.org/browse/JDK-8305814). It upgrades Xalan to 2.7.3.

It was cleanly cherry picked from b1625af600.

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### Progress
- [ ] Change must be properly reviewed (1 review required, with at least 1 [Reviewer](https://openjdk.org/bylaws#reviewer))
- [x] Change must not contain extraneous whitespace
- [ ] Commit message must refer to an issue

### Error
 ⚠️ The pull request body must not be empty.

### Reviewing
<details><summary>Using <code>git</code></summary>

Checkout this PR locally: \
`$ git fetch https://git.openjdk.org/jdk21u-dev.git pull/1907/head:pull/1907` \
`$ git checkout pull/1907`

Update a local copy of the PR: \
`$ git checkout pull/1907` \
`$ git pull https://git.openjdk.org/jdk21u-dev.git pull/1907/head`

</details>
<details><summary>Using Skara CLI tools</summary>

Checkout this PR locally: \
`$ git pr checkout 1907`

View PR using the GUI difftool: \
`$ git pr show -t 1907`

</details>
<details><summary>Using diff file</summary>

Download this PR as a diff file: \
<a href="https://git.openjdk.org/jdk21u-dev/pull/1907.diff">https://git.openjdk.org/jdk21u-dev/pull/1907.diff</a>

</details>

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Commit messages:
 - 8305814: Update Xalan Java to 2.7.3

Changes: https://git.openjdk.org/jdk21u-dev/pull/1907/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=1907&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8305814
  Stats: 77 lines in 4 files changed: 10 ins; 36 del; 31 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/1907.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/1907/head:pull/1907

PR: https://git.openjdk.org/jdk21u-dev/pull/1907