add diagnostic when KeyError is thrown by crytic-compile

[0xalpharush]

If a framework isn't cleaning its artifacts/build info it their entirety or --ignore-compile is used and the file was edited, we may hit an exception due to the offset being invalidated. We should provide a better diagnostic and suggest running the clean command

see #2296 (comment)

slither/slither/core/source_mapping/source_mapping.py

Lines 138 to 171 in e3dcf1e

	def _convert_source_mapping(
	offset: str, compilation_unit: "SlitherCompilationUnit"
	) -> Source: # pylint: disable=too-many-locals
	"""
	Convert a text offset to a real offset
	see https://solidity.readthedocs.io/en/develop/miscellaneous.html#source-mappings
	Returns:
	(dict): {'start':0, 'length':0, 'filename': 'file.sol'}
	"""
	sourceUnits = compilation_unit.source_units
	position = re.findall("([0-9]*):([0-9]*):([-]?[0-9]*)", offset)
	if len(position) != 1:
	return Source(compilation_unit)
	s, l, f = position[0]
	s = int(s)
	l = int(l)
	f = int(f)
	if f not in sourceUnits:
	new_source = Source(compilation_unit)
	new_source.start = s
	new_source.length = l
	return new_source
	filename_used = sourceUnits[f]
	# If possible, convert the filename to its absolute/relative version
	assert compilation_unit.core.crytic_compile
	filename: Filename = compilation_unit.core.crytic_compile.filename_lookup(filename_used)
	is_dependency = compilation_unit.core.crytic_compile.is_dependency(filename.absolute)
	(lines, starting_column, ending_column) = _compute_line(compilation_unit, filename, s, l)