Boxel variables consolidation

[burieberry]

What to Review: packages/boxel-ui/addon/src/styles/variables.css

Main changes:

1. Make variable names more consistent:

• use abbreviation -md instead of -med for medium
  example:
  --boxel-font-size-med --> --boxel-font-size-md
--boxel-lineheight-med --> --boxel-lineheight-md
--boxel-font-med --> --boxel-font-md
--boxel-icon-med --> --boxel-icon-md
• use the format -2xs instead of -xxs:
  example:
  --boxel-lsp-xxl --> --boxel-lsp-2xl
--boxel-border-radius-xxs --> --boxel-border-radius-2xs
--boxel-sp-xxxl --> --boxel-sp-3xl

2. Remove deprecated Boxel Purples and Boxel Neutrals (those prefixed with --boxel-purple- and --boxel-light-) and added some missing colors to the color palette:

• --boxel-150: #f4f4f4; (formerly --boxel-light-100)
• --boxel-250: #d3d3d3;
• --boxel-425: #acacac;

3. Added spacing and border-radius defaults for when card has no theme applied. this significantly improves the look even if the other variables weren't set, making the card look less broken.

Note: there is still support for the old -sp values, but slowly phasing them out.

The rest of the PR changes are replacing the places the non-supported variables are used.

[github-actions]

Host Test Results

    1 files  ±  0      1 suites  ±0   1h 1m 30s ⏱️ + 5m 39s
1 522 tests +107  1 508 ✅ +106  13 💤 +1  0 ❌ ±0  1 🔥 ±0 
1 536 runs  +107  1 519 ✅ +106  13 💤 +1  2 ❌ ±0  2 🔥 ±0 

For more details on these errors, see this check.

Results for commit c711211. ± Comparison against base commit 102bcfe.

♻️ This comment has been updated with latest results.