Use `carrier.encodePolyfill` everywhere

[krystofwoldrich]

Description

Some parts of the React Native codebase are not using the carrier.encodePolyfill but instead directly import the encoding function.

This causes inconsistencies and possible issue as changing the polyfill (for example in #4874) only affect part of the codebase.

Example of direct use of the encode function:

• sentry-react-native/packages/core/src/js/wrapper.ts

  Line 130 in f2dafa6

  const EOL = utf8ToBytes('\n');

• sentry-react-native/packages/core/src/js/wrapper.ts

  Line 167 in f2dafa6

  const headerBytes = utf8ToBytes(headerString);

• sentry-react-native/packages/core/src/js/replay/networkUtils.ts

  Line 56 in ddcabff

  return utf8ToBytes(input);