Various back ports from swiftterm

[sgmunn]

• Mostly focused on supporting esctest and back porting functionality from SwiftTerm.
• Some code shuffling to minimize some complexity and provide a way to mock and test functionality from unit tests (partially implemented).
• backport of https://github.com/migueldeicaza/SwiftTerm/pull/51
• added a test to show how we can add tests for different commands, got side tracked with parsing CSI responses but that wasn't what I was trying to test. Ended up with a simpler test but left code in to parse CSI responses since that can be used to test other responses directly.

remaining todos

~- [ ] hex mode for title~ ~- [ ] bracketedPasteMode~ (these are not fully implemented yet anyway)

• [x] csiCloseBrace
• [x] cmdSelectiveEraseRectangularArea
• [x] cmdDeleteColumns
• [x] probably others, some yak shaving

Added unit tests

• BS
• CBT
• CR
• CUP
• DECFRA (2/7)

passing esctest tests:

• CBT
• CR
• BS
• CUP
• DECSTBM
• CHA
• CHT
• CHA
• CUB
• CUD
• CUF
• CUU
• HTS
• RM
• TBC
• DCS
• DECERA
• HPR
• TBC
• SOS
• VPR
• PM
• DECFRA
• DECDSR
• DECSTR
• DECSET (14/24 - ~ swiftterm)
• VPA (3/4, same)

partial work towards https://github.com/migueldeicaza/XtermSharp/issues/69

notes:

• swiftterm at 658f7a51f33dd0b704f9a939582a049728b96925