fix(editorconfig): a custom property is treated as a section (#34445)

Problem: A custom property containing a pair of square brackets will be
treated as a section.
Solution: Change the logic parsing a section, remove the first match
regex `%b[]`.

Signed-off-by: fortime <palfortime@gmail.com>
(cherry picked from commit 966b1da183)

runtime/lua/editorconfig.lua

@@ -245,7 +245,7 @@ local function parse_line(line)
   end
 
   --- @type string?
-  local glob = (line:match('%b[]') or ''):match('^%s*%[(.*)%]%s*$')
+  local glob = line:match('^%s*%[(.*)%]%s*$')
   if glob then
     return glob
   end

test/functional/plugin/editorconfig_spec.lua

@@ -106,6 +106,10 @@ setup(function()
 
     [long_spelling_language.txt]
     spelling_language = en-NZ
+
+    [custom_properties.txt]
+    property1 = something1
+    property2 = x[something2]x
     ]]
   )
 end)
@@ -240,4 +244,20 @@ But not this one
     test_case('short_spelling_language.txt', { spelllang = 'de' })
     test_case('long_spelling_language.txt', { spelllang = 'en_nz' })
   end)
+
+  it('set custom properties', function()
+    n.exec_lua(function()
+      local editorconfig = require('editorconfig')
+      editorconfig.properties.property1 = function(bufnr, val, _opts)
+        vim.b[bufnr].property1 = val
+      end
+      editorconfig.properties.property2 = function(bufnr, val, _opts)
+        vim.b[bufnr].property2 = val
+      end
+    end)
+
+    command('edit ' .. testdir .. pathsep .. 'custom_properties.txt')
+    eq('something1', fn.luaeval('vim.b.property1'), 'property1')
+    eq('x[something2]x', fn.luaeval('vim.b.property2'), 'property2')
+  end)
 end)