Replaces the static Duplicate() method.

To make things simpler, AllocatedString is now a non-template class.

Need to check for it in iconv.h. Otherwise meson prefixes a __builtin variant in the check.

Passing `length+1` to `MultiByteToWideChar()` means the function may
fill the whole buffer with output data, and could theoretically
overwrite the null terminator.  In practice, this will never happen,
but this way, it's slightly more correct.

Also, null-terminate after `MultiByteToWideChar()`, after we got the
real output length.  Again, this would never have been a problem, but
who knows...

Using CompareStringEx() and FindNLSStringEx().

Implements a missing piece for
https://github.com/MusicPlayerDaemon/MPD/issues/820

LINGUISTIC_IGNORECASE is unimplemented on Wine, but since we don't
have any locale support (yet), and we're using LOCALE_NAME_INVARIANT,
NORM_IGNORECASE should essentially be the same, so why bother.

Reverts commit fb3564fb

LCMapStringEx() doesn't do what I imagined it would do 5 years ago.
D'oh!

Closes https://github.com/MusicPlayerDaemon/MPD/issues/820

Found with readability-uppercase-literal-suffix
Signed-off-by: Rosen Penev <rosenp@gmail.com>

None of the functions in these files come from ctype.h

Also changed one instance of isdigit to the C++ variant.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

The former was deprecated with C++14.

According to the C++11 and C++17 standards, both files are identical.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Found with readability-uppercase-literal-suffix
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Since we switched from autotools to Meson in commit
94592c14, we don't need to include
`config.h` early to properly enable large file support.  Meson passes
the required macros on the compiler command line instead of defining
them in `config.h`.

This means we can include `config.h` at any time, whenever we want to
check its macros, and there are no ordering constraints.

So long, autotools!  This is my last MPD related project to migrate
away from it.  It has its strengths, but also very obvious weaknesses
and weirdnesses.  Today, many of its quirks are not needed anymore,
and are cumbersome and slow.  Now welcome our new Meson overlords!