fix(ls): correct SymbolBody.get_text for the one-line-past-EOF range

An LSP server can end a symbol range one line past EOF: the convention
for a range covering whole lines ends it at the start of the following,
non-existent line. SymbolBody.get_text indexes self._lines[end_line]
directly, so that well-defined case raised IndexError.

get_text now corrects exactly that case (end_line == len(lines), end_col=0) to end
at the actual last line, in get_text itself so it also applies to a
cached SymbolBody, not just a freshly constructed one. Any other
out-of-range end_line now raises InvalidTextLocationError.

Fixes #1498

src/solidlsp/ls_exceptions.py

@@ -52,6 +52,15 @@ class SolidLSPException(Exception):
         return s
 
 
+class InvalidTextLocationError(SolidLSPException):
+    """
+    Raised when a symbol's LSP range refers to a text location that does not exist
+    in the file's current line buffer, other than the well-defined whole-line-through-EOF
+    convention (end line exactly one past EOF at column 0), which is corrected rather
+    than rejected.
+    """
+
+
 class MetalsStaleLockError(SolidLSPException):
     """
     Raised when a stale Metals H2 database lock is detected and the user