fix(core): resolve the tag name of dynamically created hosts - #71460

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PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• angular.dev application / infrastructure changes
• Other... Please describe:

What is the current behavior?

HOST_TAG_NAME returns '#host' when the host isn't declared in a template: root components, components rendered by <router-outlet>, ViewContainerRef.createComponent, createComponent() (with or without hostElement and directives), and hosts created by TestBed.createComponent and TestBed.createDirective. The token returns tNode.value, and the host TNode built in ComponentFactory always holds the TNodeName.DynamicHost placeholder.

DebugElement.name has the same problem: it returns '#host' for the root of every fixture and for components rendered by <router-outlet>, NgComponentOutlet or ViewContainerRef.createComponent, so fixture.debugElement.query((de) => de.name === 'app-home') doesn't find a routed component.

Issue Number: Fixes #71459

What is the new behavior?

Both now go through a getElementTagName helper in view_utils.ts: when the TNode holds the placeholder, it reads the tag name from the native element, like resolveElement in sanitization.ts already does for host bindings. I went with localName so the value matches what a template gives: lowercase for HTML, original casing for SVG (foreignObject). It falls back to tagName for renderers whose elements don't have localName. Elements declared in templates don't go through this branch, so nothing changes for them.

The new tests in di_spec.ts cover a root component, skipSelf from an element in a root component's template, ViewContainerRef.createComponent with a host directive, createComponent() with a hostElement and directives, an SVG host and TestBed.createDirective. A test in debug_node_spec.ts checks DebugElement.name on a fixture root and finds a component created through a ViewContainerRef by name. All of them fail on main with Expected '#host' to be ....

Does this PR introduce a breaking change?

• Yes
• No

Other information

One visible effect outside this repo: angular/components#30892 replaced element.tagName with HOST_TAG_NAME in MatChip. A chip created through createComponent or ViewContainerRef.createComponent gets a <mat-basic-chip> host (the first tag in its selector), so since that change it has been styled as a standard chip. With this fix it's a basic chip again, like it was before that PR.