feat(editor/copy-paste): refactor copy/export in cljs

[RCmerci]

move copy-as related codes from mldoc to cljs

• copy as text
• copy as opml
• copy as html
• old options: indent-styles, remove-emphasis, remove-page-ref-brackets
• add option: remove #tag
• replace block-reference & block-embed & page-embed

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Closes #6351

[Bad3r]

@RCmerci did you test assets export? what is the expected behaviour for local graph assets when exporting?

[RCmerci]

did you test assets export? what is the expected behaviour for local graph assets when exporting?
this export/copy feature only handles the pages/journals

[Bad3r]

this export/copy feature only handles the pages/journals
what is the expected behaviour if a page/journal contain local assets such as images?

[RCmerci]

what is the expected behavior if a page/journal contains local assets such as images?

For example, page A has content ![image](<localpath/of/this/image>), then the exported/copied content only contains the same content.
This feature mainly offers these functions:

• replace block-ref, block-embed, and page-embed with their origin contents
• some export options listed above
• copy as a different format
• and the content stays the same as the origin

[giuseppedandrea]

Hi @RCmerci! Does this refactor resolve the issue of the two trailing spaces added on each line on copy/export (#6351)?

[RCmerci]

@giuseppedandrea yes, this impl won't add 2 trailing spaces to each line

[tiensonqin]

Works great! 👍

[stdword]

@RCmerci Currently properties of blocks can't be exported (it behaved like that before your PR). The place to add another one option?

The only way to copy all text blocks tree now is via selecting root block and using keyboard: ⌘C. There is no option to Copy in context menu. Only Copy as... but it trims all the properties

[RCmerci]

@stdword This PR mainly focuses on refactoring the existing code and does not add much new functionality.
I'll definitely add 'trim properties' option to 'copy as' feature later