Add JPEG COM marker support

[RobertMut]

Prerequisites

• [x] I have written a descriptive pull-request title
• [x] I have verified that there are no overlapping pull-requests open
• [x] I have verified that I am following the existing coding patterns and practice as demonstrated in the repository. These follow strict Stylecop rules :cop:.
• [x] I have provided test coverage for my change (where applicable)

Description

This PR adds support for COM marker in JPEG as mentioned in #2067 and #2061

Implemented:

• Methods for jpeg encoder and decoder
• ICollection<Memory<char>> metadata property (#2067),
• SetComment (#2061),
• GetComment (#2061),
• ClearComments(#2061)

[CLAassistant]

All committers have signed the CLA.

[JimBobSquarePants]

Thanks for this! I'll review it asap.

[RobertMut]

I've made changes as you mentioned in PR comments. I left them open, because I don't know what the usual practice is for closing them (by the reviewer or contributor) on your repo. I hope we're on the same page. Feel free to comment if I have missed/misunderstood something or if there is a better way to do this.