refactor(view)!: improved view component rendering

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This PR fixes some long-standing issues with tempest/view. Technically it does not introduce any breaking changes, but it might lead to failed template rendering in some occasions. First, an overview of what's changing:

• Compiled templates will now use PHP's include instead of compiling everything to one file. This fixes Colliding class names in view imports #1380 when two view components import classes with the same names from different namespaces
• Namespaces can still collide, because they are passed from the parent views or view component to child view components. We provide a clear error in this case
• We've added source mapping, so that now we can refer to view source files with line number when a view compilation error occurs, fixing Improved lexer context #1194

Breaking changes

With this PR comes a refactor to the Element interface, which now requires a getImports method. However, a default implementation is provided by the IsElement trait, and thus should have no impact.

Apart from that, this PR may still lead to invalid view files with missing imports.

Let's say you have these two components:

// x-a.view.php

<?php 
use App\HomeController::class;
?>

{{ uri(HomeController::class) }}

// x-b.view.php

<?php 
use App\BlogController::class; 
use function Tempest\Router\uri;
?>

{{ uri(HomeController::class) }}

When these two view components were referenced in the same file, they would render fine before this PR:

<x-a />
<x-b />

That's because tempest views used to be compiled into one big file, and all import statements would be grouped together. However, now that we've switched to including compiled view components, the above code would break, since there's no use function Tempest\Router\uri; within the scope of <x-a>

The fix is to include uri in <x-a> as well:

// x-a.view.php

<?php 
use App\HomeController::class;
use function Tempest\Router\uri;
?>

{{ uri(HomeController::class) }}

Thanks to source-mapping, you will now get a clear exception pointing you to the source of the problem, making fixing these issues simple.

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ElementFactory now always requires a parent/root element

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Refactored parent/child setting because not all elements have children, but all have a parent.

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See before: not all elements have children but all have a parent

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Represents a block of PHP code, currently only used to extract imports

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Currently we're still using a regex, we could improve if needed once this refactor works

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This new RootElement is used as… the root.

It ensures a ViewComponentElement has a parent where it can gather imports from

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We only want to resolve imports from PhpElements, not from sibling ViewComponent elements. That's why we check instanceof PhpElement here

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View components can be nested, and we need to recursively resolve all imports.

Writing this reminds me: we also need to check for sibling PhpElements in the same file still. That's still TODO

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Refactoring to accomodate the new RootElement