fix: Wrong code generation for FieldImage

[TannerGabriel]

The basics

• I validated my changes

The details

Resolves

Fixes #2691

Other optional implementations

Alternatively, we could pass the alt and fieldRtl into the config, which is now the seventh, but I think this is the clearer approach.

new Blockly.FieldImage(src, width, height, undefined, undefined, undefined, {alt: 'star', flipRtl: true})

[gonfunko]

Thanks for the fix for this!