Fixes for `SourceFile` byte offsets

[c42f]

This fixes a crash formatting error messages when core_parse_hook is used to parse a piece of broken code with a nontrivial byte offset.

• SourceFile held by SyntaxNode preserves the indexing of the original string passed to the parse*() functions.
• Fix source_line_range and thisind accordingly

[codecov[bot]]

Codecov Report

Merging #311 (325a850) into main (ec51994) will increase coverage by 0.01%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #311      +/-   ##
==========================================
+ Coverage   96.78%   96.80%   +0.01%     
==========================================
  Files          14       14              
  Lines        4111     4125      +14     
==========================================
+ Hits         3979     3993      +14     
  Misses        132      132              

Impacted Files	Coverage Δ
src/diagnostics.jl	100.00% <ø> (ø)
src/expr.jl	100.00% <100.00%> (ø)
src/parse_stream.jl	95.41% <100.00%> (+0.03%)	:arrow_up:
src/parser.jl	98.03% <100.00%> (-0.30%)	:arrow_down:
src/parser_api.jl	93.75% <100.00%> (ø)
src/source_files.jl	97.36% <100.00%> (ø)
src/syntax_tree.jl	95.36% <100.00%> (+0.09%)	:arrow_up:

... and 2 files with indirect coverage changes