Add selectAllMatches command in column selection mode.

[Inori]

Operation flow:

1. Ctrl+F --> Open find widegt.
2. Alt+R --> Turn on regex mode.
3. Input search text --> Regex text or normal text.
4. Alt+Enter --> Select all matches.
5. Left arrow --> Ajust cursors.(Ignore this step if you don't want to edit the selected text.)
6. Edit text --> Do what you want.(Ignore this step if you don't want to edit the selected text.)
7. Shift+Home --> Select modified text.(Ignore this step if you don't want to edit the selected text.)
8. Ctrl+C --> Copy selected text.
9. Ctrl+N --> Open a new tab.
   10 .Ctrl+V --> Paste.

Compared to sublime:

[mention-bot]

By analyzing the blame information on this pull request, we identified @ajkerrigan and @alexandrudima to be potential reviewers

[msftclas]

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[msftclas]

@Inori, Thanks for signing the contribution license agreement so quickly! Actual humans will now validate the agreement and then evaluate the PR.

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[Inori]

Issues #5447

[alexdima]

@Inori Thank you, nice job! ❤️

[pcarrier]

Do we know when this will land? It's a killer feature for me and I was disappointed it's not in 1.1.0.

[taoqf]

maybe we need 'alt+f3' to select all the same words when some are selected.

[greatbody]

just like "ctrl+d" in sublime

[yisibl]

this.closeFindWidget();

Why is it removed in the latest code(in master branch)?

[akinhwan]

wow did i ever need this, man so useful thank you!!!!!!!