941 dna sequences justified

[rayzhuca]

Fixes exported SVG text being unjustified on PowerPoint.

Description

• Every SVGTextContentElement (SVGTextElement, SVGTextPath, etc.) is converted into character separated SVGTextElements
• Uses getStartPositionOfChar to get the position of individual characters in any SVGTextContentElement. However,
  getStartPositionOfChar does not carry over some specific attributes, such as dominant-baseline and transform
• dominant-baseline is calculated via dominant_baseline_matrix and get_text_height
• Due to some quirks with dart, matrix_to_map, dom_matrix_to_map, point_to_map is made to call some web API functions
• Fixed the Cannot read properties of null (reading 'toString') console error that appears immediately when website loads. (This is actually unrelated to justifying DNA sequences though.)
• Fixed export "SVG main view" viewbox bug, where on PowerPoint, for long SVGs, the SVG is cropped significantly.

Related issues

• text-shadow does not work on PowerPoint. PowerPoint does support stroke and paint-order for texts but it looks significantly worse and grainy than without it. (Notice the "A" under the modification in the PowerPoint screenshot.)
• The viewbox of an exported SVG is slightly off (line 242-248 in export_svg.dart). If you export main view the effect is significant. (Notice the domain circle "2" is cut off slightly after exporting.)

Screenshots

SVG on scadnano:

Exported SVG after "export svg text separately" option:

Exported SVG in PowerPoint: