RFR: 8343074: test/jdk/com/sun/net/httpserver/docs/test1/largefile.txt could be generated

[Volkan Yazici]

Adds `test.lib.Utils::createTempFileOfSize` to generate `test/jdk/com/sun/net/httpserver/docs` contents at runtime. This directory contains `largefile.txt` of size 2.6MiB showing up as the 4th largest file tracked by git:


$ git ls-files | while read f; do echo -e $(stat -c %s "$f")"\t$f"; done >/tmp/trackedFileSizes.txt
$ sort -n /tmp/trackedFileSizes.txt | tail -n 4
2730088	test/jdk/com/sun/net/httpserver/docs/test1/largefile.txt
2798680	src/java.base/share/data/unicodedata/NormalizationTest.txt
3574947	test/jdk/java/foreign/libTestDowncallStack.c
7128495	test/jdk/java/foreign/libTestUpcallStack.c


**Other highlights:**

- `jdk.httpclient.test.lib.common.TestUtil` is removed in favor of similar alternatives in `test.lib.Utils` and `test.lib.Asserts`
- `test.lib.Asserts::assertFileContentsEqual` is added

-------------

Commit messages:
 - Move file content assertion to `test/lib/Asserts`
 - Move HTTP-specific temp. file methods to `test.lib.Utils`
 - Replace the `docs/test1` folder with dynamically created files
 - Employ `TestUtil::assertFilesEqual` in `sun.net.httpserver` tests
 - Improve `TestUtil::getAFile`
 - Improve `TestUtil::compareFiles`

Changes: https://git.openjdk.org/jdk/pull/23401/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23401&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8343074
  Stats: 680 lines in 15 files changed: 240 ins; 277 del; 163 mod
  Patch: https://git.openjdk.org/jdk/pull/23401.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23401/head:pull/23401

PR: https://git.openjdk.org/jdk/pull/23401