ref(flamegraph): Rename STACK_TO_COLOR to stackToColor for ESLint compliance

[sentry]

This PR renames the STACK_TO_COLOR property within the flamegraph theme to stackToColor.

Why this change?
The previous STACK_TO_COLOR naming convention violated the no-capitalized-function-calls ESLint rule, which flags function calls where the callee name starts with a capital letter (conventionally reserved for constructors). The flamegraph theme's COLORS object used an ALL_CAPS convention for both constant values and callable functions, leading to this linter error when STACK_TO_COLOR was invoked.

What was changed?

• Updated the FlamegraphTheme type definition in flamegraphTheme.tsx.
• Renamed the property in both light and dark theme implementations in flamegraphTheme.tsx.
• Adjusted the return type annotation in makeStackToColor in utils/profiling/colors/utils.tsx.
• Updated all call sites in flamegraphRenderer.tsx and aggregateFlamegraphTreeTable.tsx.
• Modified the test mock in flamegraphRendererWebGL.spec.tsx to reflect the new name and removed the now-unnecessary @ts-expect-error comment.

Legal Boilerplate

Look, I get it. The entity doing business as "Sentry" was incorporated in the State of Delaware in 2015 as Functional Software, Inc. and is gonna need some rights from me in order to utilize my contributions in this here PR. So here's the deal: I retain all rights, title and interest in and to my contributions, and by keeping this boilerplate intact I confirm that Sentry can use, modify, copy, and redistribute my contributions, under Sentry's choice of terms.

Fixes CODING-CONVENTIONS-1QB