Bug/performance: No need to make repeat calls to `get_theme_file_path` in `register_block_style_handle`

[aristath]

The register_block_style_handle function runs ~200 times on each page load.
Each time it runs, we call get_theme_file_path and then run it through wp_normalize_path.
get_theme_file_path calls get_stylesheet_directory, which calls get_stylesheet, which calls get_option, and there's a bunch of filters that run on each iteration of that - without ever changing.

We can cache the value and avoid 200 calls on many functions and filters - improving performance.

Trac ticket: https://core.trac.wordpress.org/ticket/56666

@aristath Can we add this new cache related code after the if statement line no. 222? Because we required it there, not prior?

​https://github.com/WordPress/wordpress-develop/blob/d2fa335b47080abb0c7e2869687906dc32d629f0/src/wp-includes/blocks.php#L185-L189

​https://github.com/WordPress/wordpress-develop/blob/d2fa335b47080abb0c7e2869687906dc32d629f0/src/wp-includes/blocks.php#L222

[SergeyBiryukov]

In 54327:

Blocks: Remove extra get_theme_file_path() calls in register_block_style_handle().

The register_block_style_handle() function runs ~200 times on each page load. Each time it runs, we call get_theme_file_path() and then run it through wp_normalize_path().

get_theme_file_path() calls a few other functions: get_stylesheet_directory(), get_stylesheet(), get_option(), and there's a bunch of filters that run on each iteration of that, without ever changing.

By caching the value in a static variable, we can avoid ~200 calls on many functions and filters, improving performance.

Follow-up to [53091], [54290], [54291], [54309].

Props aristath, mukesh27.
Fixes #56666.

Thanks for the PR! Merged in r54327.