add goto tests for path segments and where clauses

Added goto_path_segments.fe to verify all intermediate path segments
are resolvable for goto-definition (e.g. clicking on 'stuff' in
'stuff::calculations::ambiguous' resolves correctly).

Added goto_where_clause.fe to verify trait bounds in where clauses
are resolvable (e.g. clicking on 'MyTrait' in 'where T: MyTrait'
resolves to the trait definition).

Both tests cover inline module resolution. Cross-ingot resolution
is blocked pending PR argotorg#1146 which adds ingot initialization when
opening .fe files.

Author: micahscopes

crates/language-server/test_files/goto_path_segments.fe

@@ -0,0 +1,12 @@
+mod things { pub struct Why {} }
+mod stuff {
+    pub mod calculations {
+        pub fn ambiguous() {}
+        pub mod ambiguous {}
+    }
+}
+
+fn f() {
+  let _u: things::Why
+  let _a: stuff::calculations::ambiguous
+}

crates/language-server/test_files/goto_path_segments.snap

@@ -0,0 +1,23 @@
+---
+source: crates/language-server/src/functionality/goto.rs
+expression: snapshot
+input_file: test_files/goto_path_segments.fe
+---
+0: mod things { pub struct Why {} }
+1: mod stuff {
+2:     pub mod calculations {
+3:         pub fn ambiguous() {}
+4:         pub mod ambiguous {}
+5:     }
+6: }
+7: 
+8: fn f() {
+9:   let _u: things::Why
+10:   let _a: stuff::calculations::ambiguous
+11: }
+---
+cursor position (9, 10), path: goto_path_segments::things
+cursor position (9, 18), path: goto_path_segments::things::Why
+cursor position (10, 10), path: goto_path_segments::stuff
+cursor position (10, 17), path: goto_path_segments::stuff::calculations
+cursor position (10, 31), path: goto_path_segments::stuff::calculations::ambiguous

crates/language-server/test_files/goto_where_clause.fe

@@ -0,0 +1,15 @@
+trait MyTrait {
+    fn do_something(self)
+}
+
+struct Container<T> {
+    value: T
+}
+
+impl<T> Container<T>
+    where T: MyTrait
+{
+    fn process(self) {
+        self.value.do_something()
+    }
+}

crates/language-server/test_files/goto_where_clause.snap

@@ -0,0 +1,26 @@
+---
+source: crates/language-server/src/functionality/goto.rs
+expression: snapshot
+input_file: test_files/goto_where_clause.fe
+---
+0: trait MyTrait {
+1:     fn do_something(self)
+2: }
+3: 
+4: struct Container<T> {
+5:     value: T
+6: }
+7: 
+8: impl<T> Container<T>
+9:     where T: MyTrait
+10: {
+11:     fn process(self) {
+12:         self.value.do_something()
+13:     }
+14: }
+---
+cursor position (1, 20), path: goto_where_clause::MyTrait
+cursor position (5, 11), path: goto_where_clause::Container::T
+cursor position (8, 8), path: goto_where_clause::Container
+cursor position (9, 13), path: goto_where_clause::MyTrait
+cursor position (11, 15), path: goto_where_clause::Container