[ECE] Finalize button presentation and design

[reykjalin]

Description

There are still several issues with the ECE (Stripe's Express Checkout Element) presentation that we need to work through:

Tasks

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1. [ECE] Button max-height is 55px due to constraints in Stripe's API #9006 - Here we need to update the max height across all express payment buttons in WooPayments, including ECE.
2. [ECE] Fix incorrect button widths #9005 - The ECE buttons don't have the correct width in Storefront.
3. When WooPay and ECE buttons are rendered on the same page there's an uneven gap between the buttons that we've been unable to track down.
4. Increase WooPay button label font so that it has equal prominence to competing PRBs #8136
   category: core component: WooPay focus: woopay needs design priority: medium type: enhancement +6
   

Acceptance criteria

• ECE buttons render at least as well as PRB in terms of spacing, design, sizes, responsive breakpoints, etc.
• The tasks listed in the PR description have been completed and/or fixed.

Designs

Testing instructions

See relevant issues and discussions.

Dev notes

Additional context

[pierorocca]

Hey team could we also add this issue @rafaelzaleski has picked up to this list? #8136

It would look good on the team in the feature announcement and showcase if this new implementation avoids this very noticeable font size mismatch.

[haszari]

What's ECE? Recommend defining the acronym somewhere on these issues for newbies like me :)

AHA! Express Checkout Element #8768

[bborman22]

Closing the epic for ECE design issues that were discovered. Thanks for the great work everyone!