tests/ui/lint: Move 19 tests to new non-snake-case subdir

Mainly so that it is easier to only run all `non-snake-case`-specific
tests but no other tests with:

    ./x test tests/ui/lint/non-snake-case

But also to reduce the size of the large `tests/ui/lint` directory. And
rename some tests to pass tidy, and remove them from
`src/tools/tidy/src/issues.txt`.

src/tools/tidy/src/issues.txt

@@ -2760,7 +2760,6 @@ ui/lint/issue-1866.rs
 ui/lint/issue-19102.rs
 ui/lint/issue-20343.rs
 ui/lint/issue-30302.rs
-ui/lint/issue-31924-non-snake-ffi.rs
 ui/lint/issue-34798.rs
 ui/lint/issue-35075.rs
 ui/lint/issue-47775-nested-macro-unnecessary-parens-arg.rs
@@ -2769,7 +2768,6 @@ ui/lint/issue-54099-camel-case-underscore-types.rs
 ui/lint/issue-57410-1.rs
 ui/lint/issue-57410.rs
 ui/lint/issue-63364.rs
-ui/lint/issue-66362-no-snake-case-warning-for-field-puns.rs
 ui/lint/issue-70819-dont-override-forbid-in-same-scope.rs
 ui/lint/issue-79546-fuel-ice.rs
 ui/lint/issue-79744.rs
@@ -2777,7 +2775,6 @@ ui/lint/issue-80988.rs
 ui/lint/issue-81218.rs
 ui/lint/issue-83477.rs
 ui/lint/issue-87274-paren-parent.rs
-ui/lint/issue-89469.rs
 ui/lint/issue-90614-accept-allow-text-direction-codepoint-in-comment-lint.rs
 ui/lint/issue-97094.rs
 ui/lint/issue-99387.rs

tests/ui/lint/non-snake-case/no-snake-case-warning-for-field-puns-issue-66362.stderr

@@ -1,29 +1,29 @@
 error: structure field `lowerCamelCaseName` should have a snake case name
-  --> $DIR/issue-66362-no-snake-case-warning-for-field-puns.rs:7:9
+  --> $DIR/no-snake-case-warning-for-field-puns-issue-66362.rs:7:9
    |
 LL |         lowerCamelCaseName: bool,
    |         ^^^^^^^^^^^^^^^^^^ help: convert the identifier to snake case: `lower_camel_case_name`
    |
 note: the lint level is defined here
-  --> $DIR/issue-66362-no-snake-case-warning-for-field-puns.rs:1:9
+  --> $DIR/no-snake-case-warning-for-field-puns-issue-66362.rs:1:9
    |
 LL | #![deny(non_snake_case)]
    |         ^^^^^^^^^^^^^^
 
 error: variable `lowerCamelCaseBinding` should have a snake case name
-  --> $DIR/issue-66362-no-snake-case-warning-for-field-puns.rs:20:38
+  --> $DIR/no-snake-case-warning-for-field-puns-issue-66362.rs:20:38
    |
 LL |         Foo::Good { snake_case_name: lowerCamelCaseBinding } => { }
    |                                      ^^^^^^^^^^^^^^^^^^^^^ help: convert the identifier to snake case: `lower_camel_case_binding`
 
 error: variable `anotherLowerCamelCaseBinding` should have a snake case name
-  --> $DIR/issue-66362-no-snake-case-warning-for-field-puns.rs:24:41
+  --> $DIR/no-snake-case-warning-for-field-puns-issue-66362.rs:24:41
    |
 LL |     if let Foo::Good { snake_case_name: anotherLowerCamelCaseBinding } = b { }
    |                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: convert the identifier to snake case: `another_lower_camel_case_binding`
 
 error: variable `yetAnotherLowerCamelCaseBinding` should have a snake case name
-  --> $DIR/issue-66362-no-snake-case-warning-for-field-puns.rs:27:43
+  --> $DIR/no-snake-case-warning-for-field-puns-issue-66362.rs:27:43
    |
 LL |     if let Foo::Bad { lowerCamelCaseName: yetAnotherLowerCamelCaseBinding } = b { }
    |                                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: convert the identifier to snake case: `yet_another_lower_camel_case_binding`