ci: run editorconfig-checker

[dangreen]

Why

The editorconfig job installs editorconfig-checker but never runs it: the main branch of editorconfig-checker/action-editorconfig-checker only adds the binary to PATH, and the example workflow of the action runs it in a step of its own. The job has had no such step since it was added, so it has never checked a file.

Run as is, editorconfig-checker v4.0.2 reports 91 errors, all from its indent-size rule, which wants every left-padding to be a multiple of indent_size. They are 22 CSS comments continued under their own text, 14 lines of markdown aligned with the text above them, such as the content of a list item, 3 spaces after 1. , or a wrapped column of a table, and 55 lines of the installer's Python and sh aligned with the line above, mostly commands wrapped under their first argument. .editorconfig said the rule was switched off in .editorconfig-checker.json, but that file was never added.

What

• Multi-line CSS comments take the JSDoc layout: /** and */ on lines of their own, with an asterisk at the start of every line between them. The text keeps its column, and every left-padding is even. The two comments in ImageDrop.module.css that already had this layout now open with /** instead of /*.
• Numbered list items with nested content are written as 1. followed by two spaces, so the content sits at 4 spaces instead of 3. Aligned columns in README.md and SPEC.md move one space right, to an even column, and the scores of the ranking example get a sign, +90 next to -90, so they stay right-aligned.
• Wrapped lines of the installer take a hanging indent instead of being aligned with their first argument: the line breaks after the opening bracket, and the rest goes 4 spaces deeper, 8 in the header of a compound statement as PEP 8 suggests. In setup.sh the two zenity calls continue at the column of the kdialog calls next to them, and a branch of case puts its commands on lines of their own, as does a block in make-run.sh.
• The installer section of .editorconfig reaches the files in src: its glob packages/installer/*.{py,sh} matched make-run.sh alone, so editors and the check took 2 spaces for the rest. packages/installer/**.{py,sh} gives all of them 4.
• The comment about .editorconfig-checker.json goes away.
• The step with the action is now named Install editorconfig-checker, and a new Check editorconfig step runs editorconfig-checker.

Notes

• Every indent_size stays set, so every file is checked against it.
• The Python of the installer parses to the same AST as before, its self-test passes all 56 checks, and sh -n and dash -n accept both scripts.
• The markdown parses to the same tree as before apart from the four code blocks with moved columns or signed scores, checked with mdast-util-from-markdown and its GFM extension.
• With these changes, editorconfig-checker v4.0.2 finds no errors on main.