Add apply to make macros/callables useful in filters and tests

[depoll]

Breaking change

Proposed change

This PR implements the following architectural choice: home-assistant/architecture#1221

I frequently built utility macros for myself (and am excited for the folks supplying them through HACS), but one of my biggest frustrations has been the inability to use them as filters. This change makes it possible for people building such macros to use them (and any other callable) in settings where filters may be used by adding the apply filter.

The simplest example is using a macro in a map() call:

{%- macro greet(name) -%}
Hello, {{ name }}!
{%- endmacro -%}
{{ ["Alice", "Bob"] | map('apply', greet) | list }}

Which would print ["Hello, Alice!", "Hello, Bob!"]

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)
• Deprecation (breaking change to happen in the future)
• 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 docs for as_function and apply home-assistant.io#38730
• Link to developer documentation pull request:
• Link to frontend pull request:

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
• I have followed the perfect PR recommendations
• The code has been formatted using Ruff (ruff format 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.
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• New or updated dependencies have been added to requirements_all.txt.
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To help with the load of incoming pull requests:

• I have reviewed two other open pull requests in this repository.

[abmantis]

LGTM. But since I am not too deep into templates, another pair of eyes would be nice.

[depoll]

@abmantis thanks for the review! Also worth noting that this PR was broken out from this one (in case you want to take a look -- the features are more useful together): #142033