Update documentation (README, CONTRIBUTING) for release of WordPressCS 3.0.0

[jrfnl]

README: updates for WordPressCS 3.0.0

This commit updates the README guide to be in line with WordPressCS 3.0.0.

This commit:

• Removes the "Last commit to stable" and "Nr of contributors" badges.
• Updates the "Tested on PHP..." badges.
• Updates the table of contents to match the new content of the file.
• Removes the "Project history" section (has been moved to the wiki).
• Makes the pre-requisites for the package more explicit and puts them in a separate section.
• Updates the installation instructions and adds update instructions.
  • Removes the instructions related to stand-alone installs and using composer create-project.
  • The new installation instructions take the changes in Composer 2.2 (permission required for plugins to run) into account.
  • The new installation instructions include a link to the end user/ruleset maintainer upgrade guide for WPCS 3.0.0 as the initial upgrade may need extra work.
• Updates references to the Composer PHPCS plugin to make sure these reference the new name and link to the correct GH repo (as the repo has moved).
• Removes the reference to the VIP ruleset which was removed in WPCS 2.0.0 from the "Rulesets" section.
• Adds links to the "customizable properties" section for where to find customizable properties for PHPCS native sniffs and sniffs from PHPCSExtra.
• Adds the VariableAnalysis standard and the VIP Coding Standards to the list of optional additional rulesets to use.
• Updates the command and output for the example run.
• Removes the links to IDE related tutorials in favour of a link to the wiki (to save us having to maintain this list in multiple places).
• Ensures the text consistently uses WordPressCS instead of WPCS.

Closes #481
Closes #1821
Closes #1901

CONTRIBUTING: updates for WordPressCS 3.0.0

This commit updates the CONTRIBUTING guide to be in line with WordPressCS 3.0.0.

This commit:

• Updates the information about usage of upstream sniffs and reporting upstream issues.
• Updates the information on creating a pull request.
• Removes the information about the use of a long running release PR (as we don't do this anymore in practice).
• Updates the information on running the unit tests, including the information on how to get set up with cloned dependencies.
• Updates the examples test run output and removes the outdated the asciinema image.
• Updates the code fragments and example output used in the tutorial part to be in line with the current code and run instructions.
• Ensures the text consistently uses WordPressCS instead of WPCS.
• Replaced some ablist language.

Docs: miscellaneous changes

Change WPCS to WordPressCS in miscellaneous files.

[GaryJones]

✅

[jrfnl]

Cricky.. you both are quick! Do we want to merge this already or leave it for just before the release ? I'm fine with merging it now as it won't be long for the release anymore anyway.