make: consistently use double quotes in error messages

Previously, some error messages used single quotes, very few used
backticks or parentheses, most already used double quotes.

While here, reword a few error messages to be clearer or more consistent
with related error messages.

make: use '"filename" line 123' for locations instead of 'filename:123'

The format 'filename:123' is commonly used for identifying a location in
a file. Text editors recognize it and allow quick navigation through it.
The previous format was specific to make and would have required custom
support in editors.

The new format was already used in stack traces, except for the first
line. Now all lines use the same format.

make: on error, print the targets to be made

This helps to understand situations with several nested sub-makes in
varying directories.

branches: 1.6.2;
make: show realistic invalid line in error message

Previously, the error message 'Invalid line' showed only the expanded
line, which might or might not show the actual problem. To be more
helpful, add the unexpanded line to the error message in case they
differ.

Remove the special handling of invalid lines that result from merge
conflicts. RCS is not commonly used anymore, and mentioning CVS was too
specific. By echoing the whole line, the patterns '<<<<<<' and '>>>>>>'
are clear enough to hint at the problem.

make: add more details to error message about invalid lines

tests/make: force line-based diagnostics to be listed in the tests

This way, contradictions between the intended output and the actual
output are closer together and have a better chance of being spotted.

make: fix out-of-bounds read when parsing an invalid line

Reported by Robert Morris in https://bugs.freebsd.org/265119.

Since 2021-12-14.

tests/make: add a few more tests

tests/make: extend tests for parsing makefiles