Pdf-Save: Eliminate some discrepancies between core and the plugin

The pdf-save plugin differs from core in some aspects, these are some of them:

• If a text layer is Dynamic, don't set width/height for the pango layout.

pdf_export_with_dynamic_text_box_bug

pdf_export_with_dynamic_text_box

• Letter spacing is not taken into account if it's not in the pango markup, So instead of setting it as a layout attribute, insert it in the markup (and create a markup if there is only text).

pdf_export_with_letter_spacing_bug

pdf_export_with_letter_spacing

• Take into consideration the difference between the ink rectangle extents and the logical rectangle extents by setting the offset the same as in core.

pdf_export_with_offset_not_set

pdf_export_with_offset_set

• Convert Line-Spacing and Indentation into the appropriate unit.

pdf_export_with_line_spacing_and_indentation_bug

pdf_export_with_line_spacing_and_indentation

This is partially based on Massimo's comment on issue 7092.

Closes #9220

Closes #7092

Partially fixes #2294 (I believe this addresses the letter spacing + the wrong text location (either due to not setting the offset, or due to setting the width/height for a dynamic text box), but not boldness)