Length limitation in WatchValueBoxes is an annoyance

Summary

When I create a new RAM watch, the address box does not allow me to type more characters than exist for the maximum allowed address and silently ignores any additional characters. This means that when I find a pointer, copy its value, and paste that as the address in a new watch it will be incorrect if I forgot to switch the memory domain. This leads to confusion.

Similarly, when I try to poke a value the number of characters is limited. This can make editing the value annoying, since I may want to type a new character somewhere in the number and then delete an old one. For example, put the cursor in front of the number, type 1, then delete what used to be the first character. This will fail if the prior value was already the maximum allowed length.

I think that lifting this restriction and instead displaying an error message whenever the user attempts to actually use an invalid value would be a better solution. Especially since it's already possible to enter invalid values, so the later validation should already be happening.

Repro

1. Open a core where the default memory domain is not equivalent to the emulated system's address space. (E.g. melonDS, where the default domain is Main RAM but pointers would be in the ARM9 System Bus space.)
2. Copy the value of some pointer (e.g. 217AC40)
3. Open RAM watch and click new watch
4. Paste the value from step 2 into the address field
5. Observe the incorrect value in the address field

Start by locating WatchValueBoxes and the address and value input handling described in the issue. Trace how length limits and invalid-value validation currently work, then verify that longer pasted or edited values are accepted until use and that invalid values produce an error; the issue names no tests or files to run.