brand,fonts,bootstrap - add support for weight+size+color customization

[cscheid]

Towards #10249

This adds configuration of weight + color to fonts, and fine-grained control of weight + color + family to all fonts (including distinguishing between monospace, monospace-inline and monospace-block).

[cscheid]

The tests are failing because this interacts with revealjs, so I'm going to have to do these and the revealjs in the same PR.

[cderv]

Each time we modify something in _quarto-rules.scss, we need to make sure this is also working without bootstrap.

In this PR, some new variables are used in _quarto-rules.scss and so they need to be defined either in _quarto-variables.scss or quartoDefault if the variable is dependent of a metadata for example.

_quarto-variables.scss will always be added as a default layers, bootstrap or not. So it could be used for anything that should be availabel always.

Not that it is a problem with revealjs because that is our only HTML format not using Bootstrap. But the issue is really with no bootstrap, so the issue can be reproduce using html format without bootstrap.

---
title: "Untitled"
format: 
  html:
    theme: pandoc
---

Test

==> quarto preview index.qmd --to html --no-watch-inputs --no-browse

Warning: variable used before declaration
variable:  link-color 95
ERROR: Theme file compilation failed:

Error: Undefined variable.
    ╷
478 │   font-family: $font-family-monospace-block;
    │                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    ╵

Stack trace:

Error: Undefined variable.
    ╷
478 │   font-family: $font-family-monospace-block;
    │                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    ╵
    at dartCommand (file:///C:/Users/chris/DOCUME~1/DEV_R/QUARTO~2/src/core/dart-sass.ts:101:11)
    at eventLoopTick (ext:core/01_core.js:175:7)
    at async dartCompile (file:///C:/Users/chris/DOCUME~1/DEV_R/QUARTO~2/src/core/dart-sass.ts:51:3)
    at async SassCache.setFromHash (file:///C:/Users/chris/DOCUME~1/DEV_R/QUARTO~2/src/core/sass/cache.ts:89:7)
    at async compileSass (file:///C:/Users/chris/DOCUME~1/DEV_R/QUARTO~2/src/core/sass.ts:153:18)
    at async resolveSassBundles (file:///C:/Users/chris/DOCUME~1/DEV_R/QUARTO~2/src/command/render/pandoc-html.ts:131:17)
    at async resolveExtras (file:///C:/Users/chris/DOCUME~1/DEV_R/QUARTO~2/src/command/render/pandoc.ts:1303:14)
    at async runPandoc (file:///C:/Users/chris/DOCUME~1/DEV_R/QUARTO~2/src/command/render/pandoc.ts:420:20)
    at async renderPandoc (file:///C:/Users/chris/DOCUME~1/DEV_R/QUARTO~2/src/command/render/render.ts:202:24)
    at async Object.onRender (file:///C:/Users/chris/DOCUME~1/DEV_R/QUARTO~2/src/command/render/render-files.ts:715:30)

[cderv]

Thank you. It feels a lot cleaner not modifying distribution file.