Don't use strings for `BreadcrumbType` in NDK

[lemnik]

Goal

Small reduction in overhead when leaving breadcrumbs: use integers to represent the BreadcrumbType instead of strings.

Design

While the string values for BreadcrumbType on the Java/Kotlin code were constants, they required a call to GetStringUTFChars and strcmp to evaluate which enum value to use.

The new implementation uses an exhaustive when which means:

• the transfer values are not sensitive to the ordering of the enum values (as ordinal would be)
• any adding or removing of enum values will cause compiler failures

Testing

Relied on existing tests.

[bugsnagbot]

Android notifier sizes

Format	Size impact of Bugsnag (kB)	Size impact of Bugsnag when Minified (kB)
APK	1844.24	1668.28
arm64_v8a	626.95	450.82
armeabi_v7a	561.42	385.29
x86	704.75	524.53
x86_64	671.99	495.86

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