Create Range header section in HTTP extensions section

[dlrobertson]

Create a Range header section in the HTTP extensions section and move relevant algorithms to the section (e.g. add a range header and parse a single range header). See https://github.com/whatwg/fetch/pull/1520#discussion_r1032236539 for details.

[callmetushar123]

@annevk Can you assign this to me and also can you guide me a bit?

[dlrobertson]

Note that #1520 hasn't been merged yet, so the Range header section would only contain add a range header.

[dlrobertson]

Can you assign this to me and also can you guide me a bit?

@callmetushar123 any progress on the issue? Also let me know if you're stuck and could use some pointers.