Fix tag editor preview issue due to blackslash

[thewheat]

PR details

• Currently in the Tag Editor modal we can have incorrect "Live Preview" data and this PR aims to fix it
  
• Closes [Bug] Can't load file for file token #757, Closes File paths not parsed on Windows #2563 (dupe of [Bug] Can't load file for file token #757)
• Feels that there is some complexity to this so if I went down the wrong path let me know and I'll see how I can modify this 👍

Files issue

Before

After

Base64 issue

Before

After

---

Context

• When a string with a backslash is used (e.g. in a file name or in input value of a function)
• It will work correctly on first use
  
• But closing the modal and reopening it will show that the "Live Preview" with no data / incorrect data (illustrated in the first image in this PR)

Other details

• It looks like there is escaping of strings when an input value is changed

  insomnia/packages/insomnia-app/app/ui/components/templating/tag-editor.js

  Lines 142 to 145 in 03d83a8

  	// Fix strings
  	if (typeof argValue === 'string') {
  	argValue = argValue.replace(/\\/g, '\\\\');
  	}

• This requires activeTagData.args values which are strings needing to be escaped on first load (which is the core part of this PR)
• While this PR fixes the current problem I feel that there could be something related to the escaping of strings which could be the root issue (I couldn't figure out the full context of why it needed to be escaped)

[CLAassistant]

All committers have signed the CLA.

[dimitropoulos]

Works!

(before on left, after on right)