[Bug?]: Shell drops trailing spaces in parameter expansion alternate values

Self-service

• I'd be willing to implement a fix

Describe the bug

When using parameter expansion with alternate values, trailing spaces are being dropped. For example:

FOO=hi && echo ${FOO:+hello }world

should output:
hello world

but the output is instead:
helloworld

To reproduce

await packageJsonAndInstall({
  scripts: {
    alt: "FOO=hi && echo ${FOO:+hello }world",
  },
});

expect(await yarn(`run`, `alt`)).toBe("hello world\n");

Environment

System:                                                             
  OS: Windows 10 10.0.22623                                         
  CPU: (12) x64 AMD Ryzen 5 2600 Six-Core Processor                 
Binaries:                                                           
  Node: 18.15.0 - ~\AppData\Local\Temp\xfs-d5211d86\node.CMD        
  Yarn: 4.0.0-rc.42.dev - ~\AppData\Local\Temp\xfs-d5211d86\yarn.CMD
  npm: 9.5.0 - C:\Program Files\nodejs\npm.CMD

Additional context

Running the same in a bash shell:

Start by running the supplied JavaScript reproduction with yarn run alt and compare its output with the expected hello world\n. Trace the shell parameter-expansion handling for alternate values, then add coverage for the trailing-space case and confirm the command preserves the space.