RFR: 8340580: Characters in Document diagrams not in the middle

[Alexey Ivanov]

This is a continuation to #20376, it moves the text in `Document-{insert,remove}.svg` down by 0.5 pixel.

This change makes the text centred in the boxes.

Here are quotes from https://github.com/openjdk/jdk/pull/20376#issuecomment-2353728939 and https://github.com/openjdk/jdk/pull/20376#issuecomment-2353743533:

> <q cite="https://github.com/openjdk/jdk/pull/20376#issuecomment-2353728939">At 200% scale and Arial font, there are 6 pixels on top of ‘T’ and ‘h’, but there are 8 pixels on the bottom of ‘q’.</q>
> 
> <q cite="https://github.com/openjdk/jdk/pull/20376#issuecomment-2353743533">Moving the text position by 0.5 seems to help, and the values become equal: 7 on either side.</q>

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Commit messages:
 - 8340580: Characters in Document diagrams not in the middle

Changes: https://git.openjdk.org/jdk/pull/22549/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22549&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8340580
  Stats: 39 lines in 2 files changed: 0 ins; 0 del; 39 mod
  Patch: https://git.openjdk.org/jdk/pull/22549.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22549/head:pull/22549

PR: https://git.openjdk.org/jdk/pull/22549