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: in erroneous conditions, report the non-expanded text

In a condition, when a function call expression is missing its closing
parenthesis, there's no point in having the expanded argument text in
the error message.

When parsing a bare word in a condition, the trailing space was included
in that word, which was inconsistent, as the leading space was not
included either. Removing the trailing space from the word reduces the
cases where a multiple-inclusion guard steps in, but only in an edge
case that is irrelevant in practice.

tests/make: demonstrate unintended parsing of words in conditions

A word is not supposed to include its trailing space, as it doesn't
contain its leading space either.

make: add details to error messages about missing ')'

make: error out on conditions containing the operators '&' and '|'

These abbreviated variants of the '&&' and '||' operators were never
documented, so error out in non-lint mode as well.

branches: 1.9.2;
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.

tests/make: fix documentation in cond-func.mk

make: generate more specific error message on malformed conditional

make(1): remove "warning" from missing closing parenthesis

This only affects the diagnostics for parse errors that involve a
missing closing parenthesis. Whether or not this is a parse error is
still the same.

It may look redundant to pass both the CondParser and the parsing
position pp to the functions, but that's necessary since during parsing,
not every code path updates the main parsing position immediately.

make(1): clean up some tests

Fix some mistakes in comments.

Improve some comments to be easier understandable.

Inline variables that are irrelevant for the test at hand (RUN,
MAKE_CMD).

Remove references to functions and constants that have since been removed
or renamed.

make(1): add tests for parsing conditionals, document a parsing bug

make(1): add tests for edge cases in parsing conditionals

make(1): add test for function argument with unbalanced braces

make(1): add test for parsing functions in .if conditions