DXF: Refactor out block insertion to its own function

[Alan Thomas]

Currently the OGRDXFLayer::TranslateINSERT function is the only logic that inserts blocks. However, in the future we might want to insert blocks from other places in the code; for example, arrowheads are stored as blocks.

Some of the work I am currently doing on improving OGR's support for DXF DIMENSION and LEADER entities requires the block insertion code to be refactored out into its own function.

This patch also fixes a bug (test case supplied) where the insertion point of an INSERT entity is not transformed into the OCS, as required by the DXF specification.

[Alan Thomas]

The file should display as two squares side by side

[Alan Thomas]

Patch

[Even Rouault]

In 40352:

DXF: refactor out block insertion to its own function, and transform insertion point of an INSERT entity into OCS (patch by atlight, fixes #7077)

[Even Rouault]

In 40353:

Fix compiler error and cppcheck warning (refs #7077)

[Alan Thomas]

Sorry about that, Even. MSVC doesn't complain about missing standard library headers, so it's very easy to miss it.

[Even Rouault]

In 40357:

DXF: fix memory leak. Fixes ​https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=3580. Credit to OSS Fuzz (trunk only, refs #7077)