docs(theming): Adds details around new theme and glass mode.

[edonehoo]

Makes progress on #4952 and #4951

updated https://pf-org--pr-4983-site.surge.sh/foundations-and-styles/theming
and added https://pf-org--pr-4983-site.surge.sh/foundations-and-styles/theming/glass-mode-handbook

Both of which will need Dev/Design input and validation. Will probably want some images to support the /theming docs (assume these can't be created until the tokens and kit updates are available):

• Standard page Default theme (can create now)
• Standard page Felt theme
• Before/after glass image
• Figma screenshot for swapping themes
• theme switcher/theme preferences menu example - what do we want to suggest here?

[patternfly-build]

Preview: https://pf-org--pr-4983-site.surge.sh

[edonehoo]

will want to update this to include glass

[phcox]

Just a couple of comments here on the glass mode handbook. Parts of this Opacity section seem to be at odds with the Glass design tokens table below it.

Opacity
The default opacity values used in our components have been tested for accessibility, legibility, and visual appeal.

Felt light typically utilizes a 40% opacity to maintain AAA contrast for standard text.
Felt dark utilizes a 60% opacity to provide better reliability for the dark color scheme.

Given that a variety of opacity percentages are shown in the table, this seems confusing to cite specific ones for each mode. Also, instead of "reliability" did you intend "readability"?

If a product team chooses to override these token values, they are responsible for conducting their own accessibility evaluation to ensure WCAG compliance.

I would not use "token values" in the above sentence, since you only referred to base opacity levels and not the tokens themselves.

I'm not well-versed in the actual values and tokens tha we've eventually decided on, so someone else will have to review those details.

Everything else looked good!