lexing rune cant handle backslash and newline

[SurmanPP]

Describe the bug

The lexing of the backtick syntax for runes breaks with a single backslash or a backslash and a newline.

Reproduction Steps

case 1.

a :=  `\
`

case 2.

a := `\`

case 3.

a := `\` foo bar

Expected Behavior

Case 1 and 2 should be caught in the lexer.
Case 3 should have a nicer error message. Maybe with details about escaping and telling that it can only be one rune.

Current Behavior

1. outputs C error: empty character constant
2. outputs a C error: missing terminating ' character
3. outputs V error:

invalid character literal \ foo bar
=>` foo bar
([`, ```, , `f`, `o`, `o`, ` `, `b`, `a`, `r`, `
`]) (more than one character)
1 | a := `` foo bar
| ^

Possible Solution

No response

Additional Information/Context

No response

V version

V 0.4.1 24cb98d

Environment details (OS name and version, etc.)

V full version: V 0.4.1 c85232e.24cb98d
OS: linux, Pop!_OS 22.04 LTS

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