Rewrite source mapping class

[montyly]

• Rewrite compute_line and _convert_source_mapping to be efficient:
  

  slither/slither/core/source_mapping/source_mapping.py

  Lines 17 to 58 in 8586774

  	@staticmethod
  	def _compute_line(source_code, start, length):
  	"""
  	Compute line(s) numbers and starting/ending columns
  	from a start/end offset. All numbers start from 1.
  	Not done in an efficient way
  	"""
  	source_code = source_code.encode("utf-8")
  	total_length = len(source_code)
  	source_code = source_code.splitlines(True)
  	counter = 0
  	i = 0
  	lines = []
  	starting_column = None
  	ending_column = None
  	while counter < total_length:
  	# Determine the length of the line, and advance the line number
  	line_content = source_code[i]
  	line_length = len(line_content)
  	i = i + 1
  	# Determine our column numbers.
  	if starting_column is None and counter + line_length > start:
  	starting_column = (start - counter) + 1
  	if (
  	starting_column is not None
  	and ending_column is None
  	and counter + line_length > start + length
  	):
  	ending_column = ((start + length) - counter) + 1
  	# Advance the current position counter, and determine line numbers.
  	counter += line_length
  	if counter > start:
  	lines.append(i)
  	# If our advanced position for the next line is out of range, stop.
  	if counter > start + length:
  	break
  	return lines, starting_column, ending_column

• Use fields instead of dictionary:
  

  slither/slither/core/source_mapping/source_mapping.py

  Lines 122 to 133 in 8586774

  	return {
  	"start": s,
  	"length": l,
  	"filename_used": filename_used,
  	"filename_relative": filename_relative,
  	"filename_absolute": filename_absolute,
  	"filename_short": filename_short,
  	"is_dependency": is_dependency,
  	"lines": lines,
  	"starting_column": starting_column,
  	"ending_column": ending_column,
  	}

• Remove source_mapping_str and use __str__:
  

  slither/slither/core/source_mapping/source_mapping.py

  Lines 155 to 158 in 8586774

  	@property
  	def source_mapping_str(self) -> str:
  	lines = self._get_lines_str()
  	return f'{self.source_mapping.get("filename_short", "")}{lines}'

[montyly]

Consider #743 (comment) during the refactor