indent: fix stack overflow, add more tests

For several parser symbols, 2 symbols are pushed in a row, which led to
an out-of-bounds write.

indent: compute indentation of 'case' labels on-demand

One less moving part to keep track of.

No functional change.

tests/indent: change directive from '#' to '//'

Using a '//' instead of '#' turns the directives into well-formed C
code, resulting in fewer error markers in the editor.

indent: remove FreeBSD IDs

Most of the IDs were empty anyway.

tests/indent: migrate test token_case_label to lsym_case_label

tests/indent: clean up and extend tests

tests/indent: migrate integer options tests to t_options