Keep is/extends inline for multi-argument template heritage

[oha-4]

Fixes the is-breaking part of #11009 (the blank-line/over-indent part is addressed separately in #11010).

Problem

When a model/scalar heritage clause (is X / extends X) references a template with multiple arguments, the formatter wrapped the keyword and the template reference in a single group(indent(...)). Prettier measures that group against the full flat width of the template argument list, so the group broke and pushed the keyword onto its own indented line — even when the declaration line itself was short:

model Picked
  is PickProperties<
    Sample,
    ...
  >;

Fix

printHeritageClause now keeps the keyword on the declaration line when the base is a template reference with multiple (breakable) arguments, and lets the template argument list control the line break:

model Picked is PickProperties<
  Sample,
  ...
>;

Single-argument (hugged) and non-template bases keep the previous behavior of breaking the keyword onto its own line when the declaration is too long.

Tests

• Added regression tests for the multi-argument case on model is, model extends, and scalar extends in formatter.test.ts.
• Reformatted one committed http-client-java test spec (arm-customization.tsp) that contained the old output (whitespace only, no semantic change).
• Formatter test suite, eslint, tsc, and prettier --check "**/*.tsp" all pass locally.

Note: the crossLanguageVersion hash in the corresponding *_metadata.json is whitespace-sensitive; it will be updated from the RegenCheck output once CI runs.

🤖 Generated with Claude Code

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commit: b211eb8

[github-actions]

All changed packages have been documented.

• ✅ @typespec/compiler
• ✅ @typespec/http-client-java

Show changes

@typespec/compiler - fix ✏️

Keep the is/extends keyword on the declaration line when the base is a template reference with multiple arguments. The template argument list now controls the line breaking instead of the keyword being pushed onto its own indented line.

@typespec/http-client-java - internal ✏️

Reformat a test spec affected by the compiler formatter change keeping is/extends inline for multi-argument template references (whitespace only, no semantic change).