Improved output for text selection and copy/paste

Replace text elements (block) with tspan (inline) which seem to cause new lines when copying text.

Remove all whitespace between tspan:s to not cause them to end as whitespace in copied text.

Replace figure space codepoint with normal whitespace and use xml:space="preserve" instead.
Otherwise copied text would include a confusing non-U+0020 whitespace. This also fixes an issue
with Inkscape not rendering underline for a text element with only whitespace.

Have reported bug/issue here https://gitlab.com/inkscape/inbox/-/issues/9621

Note that selecting multiple lines will currently not produce new lines i copied text.

Possibly also fixes issue in Safari with text baseline styling.

Fixes #5