[Diff] Refactor for Diff3, Git, and conflicts (#4111)

[Diff] Refactor Diff, Git Diff and Diff3

This commit...

1. rewrites Diff and Diff3 syntax according to the GNU and SVN documentation.
2. adds new Git Diff syntax, also used by Git Log.

## Notable changes

- new support for
    - Diff3 formats
    - Conflict sections
    - "Combined" unified diffs, only in Git Diff
- new syntax for Git Diff emails (`git am` and `git format-patch`)
  - if normal Diff syntax detects the "magic" first line, 
    it delegates out to Git Diff instead.
- tweaked scopes, preserving stacking from #2178 for backwards-compatibility
- lots of documentation links
- lots of new tests, mostly pulled from relevant documentation

Co-authored-by: deathaxe <deathaxe82@googlemail.com>

[Diff] Refactor for Diff3, Git, and conflicts (#4111)

[Diff] Refactor Diff, Git Diff and Diff3

This commit...

1. rewrites Diff and Diff3 syntax according to the GNU and SVN documentation.
2. adds new Git Diff syntax, also used by Git Log.

## Notable changes

- new support for
    - Diff3 formats
    - Conflict sections
    - "Combined" unified diffs, only in Git Diff
- new syntax for Git Diff emails (`git am` and `git format-patch`)
  - if normal Diff syntax detects the "magic" first line, 
    it delegates out to Git Diff instead.
- tweaked scopes, preserving stacking from #2178 for backwards-compatibility
- lots of documentation links
- lots of new tests, mostly pulled from relevant documentation

Co-authored-by: deathaxe <deathaxe82@googlemail.com>

[Diff] Refactor for Diff3, Git, and conflicts (#4111)

[Diff] Refactor Diff, Git Diff and Diff3

This commit...

1. rewrites Diff and Diff3 syntax according to the GNU and SVN documentation.
2. adds new Git Diff syntax, also used by Git Log.

## Notable changes

- new support for
    - Diff3 formats
    - Conflict sections
    - "Combined" unified diffs, only in Git Diff
- new syntax for Git Diff emails (`git am` and `git format-patch`)
  - if normal Diff syntax detects the "magic" first line, 
    it delegates out to Git Diff instead.
- tweaked scopes, preserving stacking from #2178 for backwards-compatibility
- lots of documentation links
- lots of new tests, mostly pulled from relevant documentation

Co-authored-by: deathaxe <deathaxe82@googlemail.com>

[Diff] Refactor for Diff3, Git, and conflicts (#4111)

[Diff] Refactor Diff, Git Diff and Diff3

This commit...

1. rewrites Diff and Diff3 syntax according to the GNU and SVN documentation.
2. adds new Git Diff syntax, also used by Git Log.

## Notable changes

- new support for
    - Diff3 formats
    - Conflict sections
    - "Combined" unified diffs, only in Git Diff
- new syntax for Git Diff emails (`git am` and `git format-patch`)
  - if normal Diff syntax detects the "magic" first line, 
    it delegates out to Git Diff instead.
- tweaked scopes, preserving stacking from #2178 for backwards-compatibility
- lots of documentation links
- lots of new tests, mostly pulled from relevant documentation

Co-authored-by: deathaxe <deathaxe82@googlemail.com>

[Java] Fix literal backslash in strings (#4038)

This commit removes `invalid.illegal` scope from unsupported escape sequences.

Actually `\` is interpreted literal if it doesn't start a supported escape
sequence.

The following is a valid string without illegals:

```
new Source("src\main\java\com\example\application\views\HomeView.java")
```

[Java] Fix literal backslash in strings (#4038)

This commit removes `invalid.illegal` scope from unsupported escape sequences.

Actually `\` is interpreted literal if it doesn't start a supported escape
sequence.

The following is a valid string without illegals:

```
new Source("src\main\java\com\example\application\views\HomeView.java")
```

[Java] Fix literal backslash in strings (#4038)

This commit removes `invalid.illegal` scope from unsupported escape sequences.

Actually `\` is interpreted literal if it doesn't start a supported escape
sequence.

The following is a valid string without illegals:

```
new Source("src\main\java\com\example\application\views\HomeView.java")
```

[Java] Fix literal backslash in strings (#4038)

This commit removes `invalid.illegal` scope from unsupported escape sequences.

Actually `\` is interpreted literal if it doesn't start a supported escape
sequence.

The following is a valid string without illegals:

```
new Source("src\main\java\com\example\application\views\HomeView.java")
```

[Java] Fix literal backslash in strings (#4038)

This commit removes `invalid.illegal` scope from unsupported escape sequences.

Actually `\` is interpreted literal if it doesn't start a supported escape
sequence.

The following is a valid string without illegals:

```
new Source("src\main\java\com\example\application\views\HomeView.java")
```

[Java] Fix literal backslash in strings (#4038)

This commit removes `invalid.illegal` scope from unsupported escape sequences.

Actually `\` is interpreted literal if it doesn't start a supported escape
sequence.

The following is a valid string without illegals:

```
new Source("src\main\java\com\example\application\views\HomeView.java")
```