Dolt shell should read input per character/token instead of per line

A lot of Dolt shell issues (such as #10860, #10861, #10862, possibly #10865) could be fixed if input was parsed per token (or per character, like in `sql_statement_scanner`) instead of per line.

Start by tracing how the Dolt shell currently reads input and compare that path with the per-character behavior described for `sql_statement_scanner`. The work is done when shell input is parsed per token or character rather than per line, addressing the related shell issues such as #10860, #10861, and #10862.

Written by the indexing model from the issue text.