Properly parse numbers in condition fields

Falco won't properly parse a rule like this:

---
- rule: Some Rule
  desc: Some Desc
  condition: evt.type=execve and container.image.repository = 271931939120.dkr
  output: Some output
  priority: INFO
---

This is the error when validating the rules:

Tue Mar 30 12:00:40 2021: Validating rules file(s):
Tue Mar 30 12:00:40 2021:    /home/mstemm/test.yaml
1 errors:
Compilation error when compiling "evt.type=execve and container.image.repository = 271931939120.dkr": 63: syntax error, unexpected 'dkr', expecting 'or', 'and'

The parsing of the string on the right hand side stops at the period
before the dkr. The dkr then doesn't match the grammar, resulting in the
error.

Looking at the parser implementation more closely, the problem is in the
definition of "Number":

---
-   Number = C(V "Hex" + V "Float" + V "Int") / function(n)
          return tonumber(n)
       end,
---
Note that it stops after the number, but does not have any requirement
about what follows.

This changes the definition of number to require that what follows the
number is not an identifier character. With this change, values that are
only numbers are parsed as numbers, and values that start with numbers
don't match the Number definition and are parsed as BareStrings instead.

Signed-off-by: Mark Stemm <mark.stemm@gmail.com>

userspace/engine/lua/parser.lua

@@ -204,7 +204,7 @@ local G = {
    Hex = (P("0x") + P("0X")) * xdigit ^ 1,
    Expo = S("eE") * S("+-") ^ -1 * digit ^ 1,
    Float = (((digit ^ 1 * P(".") * digit ^ 0) + (P(".") * digit ^ 1)) * V "Expo" ^ -1) + (digit ^ 1 * V "Expo"),
-   Number = C(V "Hex" + V "Float" + V "Int") / function(n)
+   Number = C(V "Hex" + V "Float" + V "Int") * - V "idStart" / function(n)
          return tonumber(n)
       end,
    String = (P '"' * C(((P "\\" * P(1)) + (P(1) - P '"')) ^ 0) * P '"' +