Auto merge of #98770 - klensy:no-string-dupes-ugly, r=cjgillot

Auto merge of #98770 - klensy:no-string-dupes-ugly, r=cjgillot

rmeta: avoid embedding `StabilityLevel::Unstable` reason multiple times into .rmeta\.rlib files

Avoids bloating size of some rmeta\rlib files by not placing default string for `StabilityLevel::Unstable` reason multiple times, affects only stdlib\rustc artifacts. For stdlib cuts about 3% (diff of total size for patched\unpatched *.rmeta files of stage1-std) of file size, depending on crates.

fixes #88180