RFR: 8355360: -d option of jwebserver command should accept relative paths

[Volkan Yazici]

Allows relative paths in the content root directory passed to the `jwebserver`. Changes apply to both the `jwebserver` executable and the `java -m jdk.httpserver` execution.

### Implementation notes

Received `Path` is first passed through `.normalize().toAbsolutePath()`, and then used. The rest of the logic is untouched. This effectively implies that

1. Parts that require an absolute path (e.g., `s.n.h.s.FileServerHandler`) kept their conditions
2. Logging, failures, etc. containing the user-provided directory will now refer to the _normalized absolute_ path instead of the user-provided one (can be relative, can be not normalized, etc.)

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Commit messages:
 - Allow relative directories in `SimpleFileServerImpl::start`

Changes: https://git.openjdk.org/jdk/pull/25113/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25113&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8355360
  Stats: 126 lines in 5 files changed: 58 ins; 20 del; 48 mod
  Patch: https://git.openjdk.org/jdk/pull/25113.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25113/head:pull/25113

PR: https://git.openjdk.org/jdk/pull/25113