Add support for half-open range patterns

[jplatte]

fn main() {
    match 5 {
        ..=1 => {}
        _ => {}
    }
}

Currently produces three syntax errors

[{
	"resource": "/home/jplatte/code/playground/src/lib.rs",
	"owner": "rustc",
	"code": {
		"value": "syntax-error",
		"target": {
			"$mid": 1,
			"external": "https://rust-analyzer.github.io/manual.html#syntax-error",
			"path": "/manual.html",
			"scheme": "https",
			"authority": "rust-analyzer.github.io",
			"fragment": "syntax-error"
		}
	},
	"severity": 8,
	"message": "Syntax Error: expected FAT_ARROW",
	"source": "rust-analyzer",
	"startLineNumber": 3,
	"startColumn": 11,
	"endLineNumber": 3,
	"endColumn": 11
}]

[{
	"resource": "/home/jplatte/code/playground/src/lib.rs",
	"owner": "rustc",
	"code": {
		"value": "syntax-error",
		"target": {
			"$mid": 1,
			"external": "https://rust-analyzer.github.io/manual.html#syntax-error",
			"path": "/manual.html",
			"scheme": "https",
			"authority": "rust-analyzer.github.io",
			"fragment": "syntax-error"
		}
	},
	"severity": 8,
	"message": "Syntax Error: expected expression",
	"source": "rust-analyzer",
	"startLineNumber": 3,
	"startColumn": 11,
	"endLineNumber": 3,
	"endColumn": 11
}]

[{
	"resource": "/home/jplatte/code/playground/src/lib.rs",
	"owner": "rustc",
	"code": {
		"value": "syntax-error",
		"target": {
			"$mid": 1,
			"external": "https://rust-analyzer.github.io/manual.html#syntax-error",
			"path": "/manual.html",
			"scheme": "https",
			"authority": "rust-analyzer.github.io",
			"fragment": "syntax-error"
		}
	},
	"severity": 8,
	"message": "Syntax Error: expected `,`",
	"source": "rust-analyzer",
	"startLineNumber": 3,
	"startColumn": 12,
	"endLineNumber": 3,
	"endColumn": 12
}]

Half-open range patterns were stabilized for 1.66 in rust-lang/rust#102275.

[jonas-schievink]

To fix this, this function needs to be rewritten slightly to handle range patterns without a lower bound (left-hand side):

rust-analyzer/crates/parser/src/grammar/patterns.rs

Line 64 in 34e654c

fn pattern_single_r(p: &mut Parser<'_>, recovery_set: TokenSet) {

Then parsing for ..1 and ..=1 can be implemented and added to the test in the function.

[msfjarvis]

I'd like to try working on this

@rustbot claim

[msfjarvis]

I've been unable to make much progress and with the 1.66 release being fairly close it'd be better to let someone more experienced get to this soon.

@rustbot release-assignment