Error patterns in UI tests do not allow normalized placeholders

[pierwill]

For example, consider this test code:

rust/src/test/ui/symbol-names/const-generics-str-demangling.rs

Lines 38 to 42 in efd0483

	#[rustc_symbol_name]
	//~^ ERROR symbol-name(_RMs3_Csno73SFvQKx_1cINtB3_3StrKRef09f908af09fa688f09fa686f09f90ae20c2a720f09f90b6f09f9192e29895f09f94a520c2a720f09fa7a1f09f929bf09f929af09f9299f09f929c_E)
	//~| ERROR demangling(<c[464da6a86cb672f]::Str<"🐊🦈🦆🐮 § 🐶👒☕🔥 § 🧡💛💚💙💜">>)
	//~| ERROR demangling-alt(<c::Str<"🐊🦈🦆🐮 § 🐶👒☕🔥 § 🧡💛💚💙💜">>)
	impl Str<"🐊🦈🦆🐮 § 🐶👒☕🔥 § 🧡💛💚💙💜"> {}

After normalization of this to read

 #[rustc_symbol_name] 
 //~^ ERROR symbol-name(_RMs3_CsCRATE_HASH_1cINtB3_3StrKRef09f908af09fa688f09fa686f09f90ae20c2a720f09f90b6f09f9192e29895f09f94a520c2a720f09fa7a1f09f929bf09f929af09f9299f09f929c_E) 
 //~| ERROR demangling(<c[HASH]::Str<"🐊🦈🦆🐮 § 🐶👒☕🔥 § 🧡💛💚💙💜">>) 
 //~| ERROR demangling-alt(<c::Str<"🐊🦈🦆🐮 § 🐶👒☕🔥 § 🧡💛💚💙💜">>) 
 impl Str<"🐊🦈🦆🐮 § 🐶👒☕🔥 § 🧡💛💚💙💜"> {} 

one must truncate the entire annotation, or the test will fail, even if the correct, normalized output is in the .stderr file.

See the discussion in #89836 (comment).