Fix inline image issues

[croqaz]

This PR fixes 2 issues:

• fix img.complete being false, which breaks inline image feature completely EDIT: this solution was not good, see the comments
  It seems that immediately after you set image.crossOrigin = 'anonymous' the image becomes "not loaded yet", which breaks the logic. It's easy to check just by adding a quick console.log('IMAGE:', img, img.complete, img.naturalWidth, img.naturalHeight) just before this if condition:

  rrweb/packages/rrweb-snapshot/src/snapshot.ts

  Lines 534 to 535 in b0dc388

  	if (image.complete && image.naturalWidth !== 0) recordInlineImage();
  	else image.onload = recordInlineImage;

  
  I moved that logic just before we call toDataURL() just like this article says: https://developer.mozilla.org/en-US/docs/Web/HTML/CORS_enabled_image

• remove srcset which overwrites the src and breaks restoring images that have srcset

ping @Mark-Fenng because you have the context of this feature from previous PR.