RFR: 8358688: HttpClient: Simplify file streaming in RequestPublishers.FilePublisher [v3]

[Volkan Yazici]

> Simplifies content streaming for `HttpRequest.BodyPublishers::ofFile(Path)`, which delegates to `RequestPublishers.FilePublisher::create(Path)`. This effectively replaces all usages of `FileInputStream::new` in `HttpClient` with `Files::newInputStream(Path)`. See the JBS ticket description for the full story.
> 
> Also removing certain test files which were rendered redundant after `SecurityManager` removal. We do this in this PR, since tests were added due to touched lines.
> 
> `tier1,2` results on b5f3c8dc6f4 are attached to the ticket.

Volkan Yazici has updated the pull request incrementally with one additional commit since the last revision:

  Update tests

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Changes:
  - all: https://git.openjdk.org/jdk/pull/25662/files
  - new: https://git.openjdk.org/jdk/pull/25662/files/0a7800ab..9fce1c3b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25662&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25662&range=01-02

  Stats: 29 lines in 2 files changed: 23 ins; 0 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/25662.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25662/head:pull/25662

PR: https://git.openjdk.org/jdk/pull/25662