fix(lsp): better handling of "*" configs

Problem:

If a config name contains "*" it causes rtp discovery of `lsp/` to
consider the `*` as a wildcard and could lead to strange and unintended
behaviour. For example, accessing the `'*'` config from a `lsp/` file
would cause an infinite loop.

Solution:

- Explicitly disallow a config name from containing wildcards, with the
  exception of `'*'`.
- When Resolving `'*'` config, skip the rtp step.

test/functional/plugin/lsp_spec.lua

@@ -6449,5 +6449,36 @@ describe('LSP', function()
         end)
       )
     end)
+
+    it('does not allow wildcards in config name', function()
+      local err =
+        '.../lsp.lua:0: name: expected non%-wildcard string, got foo%*%. Info: LSP config name cannot contain wildcard %("%*"%)'
+
+      matches(
+        err,
+        pcall_err(exec_lua, function()
+          local _ = vim.lsp.config['foo*']
+        end)
+      )
+
+      matches(
+        err,
+        pcall_err(exec_lua, function()
+          vim.lsp.config['foo*'] = {}
+        end)
+      )
+
+      matches(
+        err,
+        pcall_err(exec_lua, function()
+          vim.lsp.config('foo*', {})
+        end)
+      )
+
+      -- Exception for '*'
+      pcall(exec_lua, function()
+        vim.lsp.config('*', {})
+      end)
+    end)
   end)
 end)