WP_Block_Processor should indicate that inner HTML matches no block type.

[dmsnell]

When the Block Processor was introduced there was a latent bug in the is_block_type() method. It misreports the block types when inner HTML is involved, as it was written before the concepts of inner HTML and top-level freeform content were separated.

It should only report block type matches for actual block delimiters and for top-level freeform content.

Trac ticket: Core-64485

## Status

• [ ] Add unit tests exposing the bug and demonstrating the fix.

## Summary

Previously, the WP_Block_Processor class was making a mistake in mis-reporting whether a token matches a block type when #innerHTML spans are involved.

This patch fixes the logic, which was originally written before a distinction between inner HTML and top-level freeform content was built.

[dmsnell]

In 61452:

Block Processor: Fix is_block_type() for inner HTML

Previously, the WP_Block_Processor class was making a mistake in
mis-reporting whether a token matches a block type when #innerHTML spans
are involved.

This patch fixes the logic, which was originally written before a
distinction between inner HTML and top-level freeform content was built.

Developed in ​https://github.com/WordPress/wordpress-develop/pull/10701
Discussed in https://core.trac.wordpress.org/ticket/64485

Fixes #64485.