Added performance manual tests

[mlewand]

Suggested merge commit message (convention)

Type: Added performance manual tests. Closes #5880.

---

Additional information

I'm pretty positive that we should disable the CKE5 inspector for these tests, as it has a noticeable impact on the results, while it is not relevant for CKEditor 5 end user. But I'd like to clarify this before I implement this.

Other notes:

• The fixtures are shared across the tests.
• The editors with the exception of rich editor use the same feature preset.

In the end we decided to do this task in a single pull request, rather than series of micro PRs, so there are a few changes;

$ git diff --stat master
 tests/_data/full-websites-styled.html         | 5254 +++++++++++++++++++
 tests/_data/large.html                        | 6718 +++++++++++++++++++++++++
 tests/_data/medium.html                       | 1535 ++++++
 tests/_data/small-inline-css.html             |  347 ++
 tests/_data/small.html                        |   18 +
 tests/_utils/utils.js                         |  122 +-
 tests/manual/performance/editorinit.html      |    6 +-
 tests/manual/performance/editorinit.js        |   76 +-
 tests/manual/performance/multipleeditors.html |    9 +
 tests/manual/performance/multipleeditors.js   |   77 +
 tests/manual/performance/multipleeditors.md   |    7 +
 tests/manual/performance/paste.html           |    8 +
 tests/manual/performance/paste.js             |   30 +
 tests/manual/performance/paste.md             |    5 +
 tests/manual/performance/richeditor.html      |   37 +-
 tests/manual/performance/richeditor.js        |   22 +-
 tests/manual/performance/richeditor.md        |    2 +
 tests/manual/performance/setdata.html         |    4 +-
 tests/manual/performance/setdata.js           |   42 +-
 22 files changed, 14189 insertions(+), 135 deletions(-)

[jodator]

I've removed the automatic CKEditor Inspector attachment as in performance, like in memory leak, debugging we should minimise the external noise.