Fix SingleMapping.spanFor to use previous line

[rakudrama]

When the generated code position is on a line that has sourcemap entries, but it is before any entry on that line, the original source position is specified by the last entry of the previous generated code line. The bug being fixed is that when these conditions held, the generated code position was incorrectly considered to be unmapped.

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[github-actions]

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Package	Version	Status	Publish tag (post-merge)
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[gemini-code-assist]

Code Review

This pull request correctly fixes an issue in SingleMapping.spanFor where a generated code position before any sourcemap entry on a line was considered unmapped. The new _findEntry method correctly implements the specified behavior of using the last entry from the previous line in such cases. The accompanying test case update properly validates this fix.

My review includes a couple of minor suggestions to correct the links to the sourcemap specification in the changelog and in a documentation comment, as they currently point to an incorrect ECMA standard.

[github-actions]

PR Health

Breaking changes ✔️

Package	Change	Current Version	New Version	Needed Version	Looking good?
source_maps	None	0.10.13	0.10.14-wip	0.10.13	✔️

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File	Coverage
pkgs/source_maps/lib/parser.dart	💚 63 %

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pkgs/bazel_worker/benchmark/benchmark.dart
pkgs/benchmark_harness/integration_test/perf_benchmark_test.dart
pkgs/boolean_selector/example/example.dart
pkgs/clock/lib/clock.dart
pkgs/clock/lib/src/clock.dart
pkgs/clock/lib/src/default.dart
pkgs/clock/lib/src/stopwatch.dart
pkgs/clock/lib/src/utils.dart
pkgs/clock/test/clock_test.dart
pkgs/clock/test/default_test.dart
pkgs/clock/test/stopwatch_test.dart
pkgs/clock/test/utils.dart
pkgs/coverage/lib/src/coverage_options.dart
pkgs/html/example/main.dart
pkgs/html/lib/dom.dart
pkgs/html/lib/dom_parsing.dart
pkgs/html/lib/html_escape.dart
pkgs/html/lib/parser.dart
pkgs/html/lib/src/constants.dart
pkgs/html/lib/src/encoding_parser.dart
pkgs/html/lib/src/html_input_stream.dart
pkgs/html/lib/src/list_proxy.dart
pkgs/html/lib/src/query_selector.dart
pkgs/html/lib/src/token.dart
pkgs/html/lib/src/tokenizer.dart
pkgs/html/lib/src/treebuilder.dart
pkgs/html/lib/src/utils.dart
pkgs/html/test/dom_test.dart
pkgs/html/test/parser_feature_test.dart
pkgs/html/test/parser_test.dart
pkgs/html/test/query_selector_test.dart
pkgs/html/test/selectors/level1_baseline_test.dart
pkgs/html/test/selectors/level1_lib.dart
pkgs/html/test/selectors/selectors.dart
pkgs/html/test/support.dart
pkgs/html/test/tokenizer_test.dart
pkgs/html/test/trie_test.dart
pkgs/html/tool/generate_trie.dart
pkgs/pubspec_parse/test/git_uri_test.dart
pkgs/stack_trace/example/example.dart
pkgs/watcher/test/custom_watcher_factory_test.dart
pkgs/yaml_edit/example/example.dart

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[sigmundch]

Since the refactor_test only covered this behavior indirectly, it may be helpful to add a test case in parser_test.dart to cover this scenario.

[rakudrama]

I have added a test that used to fail like this, but now passes:

00:00 +28 -4: test/continued_region_test.dart: continued span, later line, later column [E]        
  Expected: '----------\n'
              '----------\n'
              '----AAAAAA\n'
              'AAAAAAAAAA\n'
              'AAAAAAAAAA\n'
              'AAAAAABBBB\n'
              'BBBBBBBBBB\n'
              'BBBBBBBBBB\n'
              ''
    Actual: '----------\n'
              '----------\n'
              '----AAAAAA\n'
              'AAAAAAAAAA\n'
              'AAAAAAAAAA\n'
              '------BBBB\n'
              'BBBBBBBBBB\n'
              'BBBBBBBBBB\n'
              ''
     Which: is different.
            Expected: ... AAAAAAAA\nAAAAAABBBB ...
              Actual: ... AAAAAAAA\n------BBBB ...
                                    ^
             Differ at offset 60

[sigmundch]

Thank you @rakudrama!

[sigmundch]

nit: s/file file/file/