fix(material/toolbar): reset heading typography styles inside toolbar

[EduardF1]

Fixes #26261

Summary

Headings (h1 to h6) placed inside mat-toolbar inherit the .mat-typography heading styles instead of the toolbar's own title typography, so they get the hierarchy font size and a bottom margin. The toolbar rule .mat-toolbar h1 and the typography rule .mat-typography h1 have the same specificity (0-1-1), so the winner depends on CSS load order, and in the common setup (mat-typography on body, component styles loaded earlier) the typography rule wins.

Change

src/material/toolbar/toolbar.scss:

• The toolbar title typography tokens (font-family, font-size, line-height, font-weight, letter-spacing) now live on .mat-toolbar itself.
• Headings are reset through a doubled class selector, .mat-toolbar.mat-toolbar h1, ... h6 (specificity 0-2-1), with font: inherit, letter-spacing: inherit and margin: 0, so they always take the toolbar typography regardless of stylesheet order.

Before / after

• Before (issue repro, mat-typography on body, <h1> inside <mat-toolbar>): the heading renders at the .mat-typography h1 size with a bottom margin.
• After: the heading renders with the toolbar title typography and no margin.

Compatibility note

The heading selector moves from specificity 0-1-1 to 0-2-1. Application styles that override heading typography inside a toolbar with a single-class selector (for example .app-header h1 { font-size: 24px }) will need a stronger selector or the --mat-toolbar-title-text-size token override. There is no API change.

Validation

• pnpm exec stylelint "src/material/toolbar/toolbar.scss" --config .stylelintrc.json
• pnpm exec sass --load-path=node_modules src/material/toolbar/toolbar.scss
• pnpm exec prettier --check src/material/toolbar/toolbar.scss
• Manual check against the StackBlitz repro from bug(mat-toolbar): mat-toolbar styles for elements like h1, h2, ... are not taking precedence over mat-typography #26261 and in src/dev-app/toolbar with mat-typography applied to body.

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[EduardF1]

Update: I have already signed the Google CLA with fischerszavarduard@gmail.com, and I have now rewritten this PR commit so the author/committer email matches that signed address. The cla/google check is still failing. Could a maintainer please re-run or investigate?

[EduardF1]

Ah, the \cla/google\ check is still failing despite my earlier re-write to match my signed CLA email. I'll wait for a maintainer to investigate or manually approve. Thank you!

[EduardF1]

@googlebot I signed it!