Add EntityFeature enum to Humidifier

[frenck]

Breaking change

Developers only: The use of the following constants has been deprecated:

• SUPPORT_MODES

Use the new HumidifierEntityFeature IntEnum instead.

Proposed change

This PR introduces the HumidifierEntityFeature, containing all the supported feature flags of a Humidifier.

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue:
• Link to documentation pull request: Add EntityFeature enum to Humidifier developers.home-assistant#1270

Checklist

• The code change is tested and works locally.
• Local tests pass. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• I have followed the development checklist
• The code has been formatted using Black (black --fast homeassistant tests)
• Tests have been added to verify that the new code works.

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated for www.home-assistant.io

If the code communicates with devices, web services, or third-party tools:

• The manifest file has all fields filled out correctly.
  Updated and included derived files by running: python3 -m script.hassfest.
• New or updated dependencies have been added to requirements_all.txt.
  Updated by running python3 -m script.gen_requirements_all.
• For the updated dependencies - a link to the changelog, or at minimum a diff between library versions is added to the PR description.
• Untested files have been added to .coveragerc.

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[probot-home-assistant]

Hey there @home-assistant/core, mind taking a look at this pull request as it has been labeled with an integration (demo) you are listed as a code owner for? Thanks!
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[probot-home-assistant]

Hey there @home-assistant/core, @Shulyaka, mind taking a look at this pull request as it has been labeled with an integration (humidifier) you are listed as a code owner for? Thanks!
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[Shulyaka]

Looks good! Thanks!