Also, add other features that were missing.

These functions scan through the entire test file every time to find the
right section, so they can be slow for large test files.

Ref: #10818

Unlike some other languages that just copy a pointer, perl copies the
entire array contents which takes time for a large array.

Ref: #10818

Namely:
- Verify that this test case should be run
- Start the servers needed to run this test case
- Check that test environment is fine to run this test case
- Prepare the test environment to run this test case
- Run the test command
- Clean up after test command
- Verify test succeeded

Ref: #10818

This takes it from a 1200 line behemoth into something more manageable.
The content and order of the functions is taken almost directly from
singletest() so the diff sans whitespace is quite short.

Ref: #10818

Ref: #10818

This simplifies error handling in the test verification code and makes
it more consistent.

Ref: #10818

Use the feature map stored in the hash table instead. Most of the
variables were only used only once, to set the value in the hash table.

Ref: #10818

The refactored code calls these functions with the same arguments more
often, so this prevents redundant test case file parsing.

Approved-by: Daniel Stenberg
Ref: #10818
Closes #10833

It's actually been this way since at least 2012 (when a 3-argument open
was added to runtests.pl). Given the lack of complaints in the interim,
it's safe to call this 23 year old perl version the minimum.

Not all warnings are fixed; many are as much stylistic suggestions than
anything and IMHO don't do much to actually improve the code.

Ref: #10818
Closes #10861

The perl 2-argument open has been considered not-quite-deprecated since
the 3-argument form was introduced almost a quarter century ago.

It hadn't been updated in 9 years; it's time.