Diagnostic to flag cases where control flow can break content projection

[crisbeto]

Note: this is a resubmit of #52726.

These changes are a follow-up to the fix from #52414. They add a new diagnostic to the compiler that will flag cases where an element would've been projected into a specific slot of a component, but it isn't because it exists inside of a control flow node that has multiple root nodes. Aside from the diagnostic, I have to move some code around so it can be reused. Includes the following commits:

refactor(compiler): expose utility for creating CSS selectors from AST nodes

When doing directive matching in the compiler, we need to be able to create a selector from an AST node. We already have the utility, but these changes simplify the public API and expose it so it can be used in compiler-cli.

refactor(compiler-cli): expose ng-content selectors and preserveWhitespaces during template type checking

These changes expose the ngContentSelectors and preserveWhitespaces metadata to the TCB so they can be used in the next commit to implement a new diagnostic.

test(core): add tests for control flow content projection with ng-container

The control flow projection diagnostic will mention ng-container as a workaround for projection multiple nodes. These changes add a couple of tests to ensure that the approach works.

fix(compiler-cli): add diagnostic for control flow that prevents content projection

This is a follow-up to the fix from #52414. It adds a diagnostic that will tell users when a control flow is preventing its direct descendants from being projected into a specific component slot.

[crisbeto]

Passing TGP

[dylhunn]

reviewed-for: public-api

[jessicajaniuk]

reviewed-for: public-api

[pkozlowski-opensource]

This PR was merged into the repository by commit 4c1d69e.

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