Add CSV.parse - Support Headers

[Zeljko-Predjeskovic]

Based on issue #15170 requirements and solution recommendations.

closes #15170, if this PR is accepted and merged.

[Zeljko-Predjeskovic]

realizing that this is not a good place since it parses the remaining rows and that means that every row could be the headers. Didnt notice since i tested only CSV and not the parser itself. Either when using this methode, rewind the parser to the begining or somehow extract the header.

[RX14]

I'm a bit dubious about rewinding to get the headers. I think the caller can make sure the CSV parser is where it needs to be before calling to_h.

[jgaskins]

I don't know how I feel about parse_to_h as a name. It's returning an array, so anything to_h seems misleading.

Is there a reason not to return Array(CSV::Row) instead of Array(Hash(String, String))? CSV::Row has the hash-like and array-like interface.

[jgaskins]

• the early return can avoid any heap allocations
• starting with an empty hash results in log(n) allocations, but since we already know how many entries the hash will be, we can allocate that many elements so we only do 1 allocation

Suggested change

	h = {} of String => String
	row.empty? ? return nil : headers.each_with_index { |header, i| h[header] = row[i] }
	return nil if row.empty?
	h = Hash(String, String).new(initial_capacity: headers.size)
	headers.each_with_index { |header, i| h[header] = row[i] }