The "1.0" concept since changed to "2.0", so replace all 1.0 below with 2.0

Description

This issue is just to summarize some of the API considerations we need to make a decision on for the 1.0 release. Please edit and add any additional items I may have forgotten (most of these I copied over from the scikit-image API 1.0 "project" under the Projects tab).

Summary of various proposed Scikit-image API changes to consider for 1.0

Module deprecations

• remove skimage.viewer: issue #?
  could then close >10 issues: https://github.com/scikit-image/scikit-image/issues?q=is%3Aissue+is%3Aopen+viewer

• remove most code in skimage.io, leaving only a thin imageio wrapper: Deprecate (most of) skimage.io in favour of imageio #5036

Function/module moves

• Update RAG functions and move them out of skimage.future: Update API for skimage.future.graph.RAG #1696
  additional issues related to RAG: https://github.com/scikit-image/scikit-image/issues?q=is%3Aissue+is%3Aopen+RAG

Parameter removal

• Juan proposed removing preserve_range altogether in 1.0 (always using the preserve_range=True behavior)
  Improved gaussian filter and convert_to_float(#5195) #5281 (comment)

parameter/function renaming

• Need to decide on random_seed vs. seed vs. sample_seed: API consistency: seed vs random_seed vs sample_seed #5359

• Need to decide on n_jobs vs. workers vs. num_workers vs. ncpu, etc: Terminology: n_jobs vs num_workers vs ncpu etc. #4876

• Need to decide on max_iter vs. niter vs. iterations. Also selem vs. structure vs. footprint: Define standard common argument's names #4154

• label_image vs labels as a parameter name: issue #?

• Harmonizing structure element API to use radius or similar name: Size of structuring elements a bit inconsistent #4536

• Rename img_as_* to rescale_to_* or convert_to_*: Rename conversion functions rescale_to_* #1234

• Many regionprops are renamed in Introduce a consistent naming scheme for measure.regionprops #5254 (corresponding to issue regionprops: rename equivalent_diameter -> equivalent_diameter_area #4821)
  The old names are still recognized so this should not be a breaking change

Misc

• audit usage of img_as_float: Code audit: usage of img_as_float #3373
  Requires some work to further verify which functions have scale-dependent default parameters, etc.

• Fixes for data types and other common sources of errors: Fixes for data types and other common sources of errors #3009
  involves more prominent and extended version of https://scikit-image.org/docs/stable/user_guide/data_types.html