Folds the two source-map config cases into a single multi-config that
exercises every parser.exportType (link, text, style, css-style-sheet)
with and without less-loader (8 configurations total). Each config
aliases STYLE_UNDER_TEST to either style.css or style.less so the
shared index.js handles all combinations.

Validation now matches what Chrome DevTools requires to actually load
a map: the //# sourceMappingURL annotation in the bundle, the V3
schema (version, sources, mappings, sourcesContent length), every
segment decoded through a base64-VLQ parser with bounds checking on
source/name indices, and an additional pass through Node's built-in
node:module SourceMap consumer to confirm at least one entry resolves.
For the less-loader path the test asserts the original .less text
(@brand-color and friends) is what lands in sourcesContent, not the
post-less compiled CSS.

Coverage for the text exportType + inline data URI source map is fully
subsumed by test/configCases/css/source-map-export-types, which now
runs all four exportType values both with and without less-loader.

`findEntry(0, 0)` returns `{}` for empty or structurally invalid
maps too, so the assertion was passing trivially without catching
anything the hand-written VLQ decoder and structural checks weren't
already catching. Removing the dependency also avoids coupling the
config case to the `node:module` `SourceMap` API.

For text/style/css-style-sheet exportTypes the CSS module is emitted
as a JS string literal. After replacing SourceMapSource with RawSource
for the inline data URI fix, the bundle's JS source map no longer
included that wrapper module at all — DevTools showed only
./index.js, the runtime, and the bootstrap. Wrap the JS literal in
OriginalSource keyed by module.identifier() so the wrapper appears
as a source alongside other JS modules. Tests assert the CSS module
identifier is in jsMap.sources for every non-link config.

Previously only the inner JS string literal was wrapped, so the
bundle's JS source map sourcesContent for the CSS module entry was
the bare JSON-stringified CSS, not the actual emitted JS. Now the
entire generated module body — `__webpack_require__.r(module.exports
= { "default": "…" })` for text, the `cssInjectStyle(<id>, "…")`
runtime call for style, and the `new CSSStyleSheet()` IIFE for
css-style-sheet — is the source under the CSS module identifier,
matching what css-loader produces.

Tests assert the wrapper text (webpack runtime calls, `module.exports`
for text, `new CSSStyleSheet()` / `replaceSync` for css-style-sheet)
shows up in sourcesContent and that it does not start with a quote
character (which would indicate the old bare-literal regression).

A CSS module's raw `module.identifier()` embeds the absolute
filesystem path (e.g. `css/auto|/home/user/.../style.css|text`)
when no loader is in front of it, so passing it directly to
OriginalSource leaked absolute paths into the bundle's JS source map
`sources` for plain `.css` builds. Regular JS sources go through
`requestShortener` and end up as `webpack:///./module.js` — switch
the CSS module emit to `module.readableIdentifier(requestShortener)`
so its sources match (`webpack:///css ./style.css (exportType: text)`,
`webpack:///css ./style.less (exportType: style)`, etc.).

Add a regression assertion that strips the `webpack:///` scheme from
each source and rejects anything starting with `/` or a Windows
drive prefix.

`SourceMapDevToolPlugin` strips `sourcesContent` from the external
maps when devtool is `nosources-*-source-map`, but the inline data URI
map we embed in the CSS string for text/style/css-style-sheet
exportTypes was generated by the CSS generator on its own and was
still carrying the original CSS body. Read
`compilation.options.devtool` and drop `sourcesContent` from the
inline map when the devtool string includes `nosources`, matching the
external behavior.

Adds test/configCases/css/nosources-source-map-export-types covering
all four exportTypes: asserts the .css.map (link), the JS .map, and
the embedded data URI map all have null/empty sourcesContent and that
no original CSS rule text leaks through any of them.