sort: Allow sorting of arbitrarily long lines

[tcl3]

With this PR sort can now handle arbitrarily long lines. Previously, lines would be truncated at 4096 bytes.

My implementation of this feature avoids string allocations when building Line objects.

I have also replaced all remaining usages of DeprecatedString with StringView

Tested with lines up to 1MB.

[tcl3]

I'm going to mark this as a draft, while I investigate the best way to process files one line at a time.