Investigate why wasm-merge + wasm-opt output is larger than the corresponding monolithic module processed with wasm-opt #8910

Recently, we experimented with applying wasm-merge and wasm-split to a Compose Multiplatform application using different Kotlin compilation modes as input. More detailed results are available here.

The results most relevant to this issue are:

• Original Opt × Monolith: 6,159,539 bytes
• Merged Opt × Closed World: 6,589,864 bytes

As shown above, the second binary is larger. It would be useful to investigate the reasons for this difference and suggest possible improvements on both on Binaryen and Kotlin sides.