[dcmtk] builtin oficonv data

[xb284524239]

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[BillyONeal]

It seems like the feature is broken; it needs to be 'internal dict' rather than 'external dict', since an external one is respected even if the internal one is available: https://support.dcmtk.org/docs/file_install.html

OFICONV DATA FILES
==================

When oficonv is used to implement character set conversion (which is the
default, starting with DCMTK 3.6.8), then a set of binary data files containing
mapping tables are used during the conversion process.  By default, these are
installed and expected in DCMTK's data path ("/usr/local/share/dcmtk-<VERSION>/
data") in the subdirectories "esdb" and "csmapper".  The data path can be
overridden at runtime by setting the environment variable "DCMICONVPATH" to
point to a different directory.

It is possible to embed the mapping tables into the oficonv library, in which
case no external files are needed at runtime.  This can be enabled by setting
the CMake variable "DCMTK_ENABLE_BUILTIN_OFICONV_DATA" to "ON".  This behavior
is enabled by default when DCMTK is compiled into shared libraries (option
"BUILD_SHARED_LIBS" set to "ON"), and disabled by default otherwise.  Note that
when using static libraries, the built-in mapping tables will increase the size
of each executable by ca. 4 MBytes.

The "DCMICONVPATH" environment variable is respected even when built-in mapping
tables are available.  In this case, the files referred to by "DCMICONVPATH"
override the built-in files, unless "DCMICONVPATH" points to DCMTK's default
data path.

That said, the feature isn't being added by this change, so I'm going to take this as is. Would really appreciate another change which flips the sense though.

Thanks!